Don't allow one to pass into setuptools_dso.setup() e.g. build_ext that
does not inherit from setuptools_dso.build_ext.

Fixes: 67d717a6 (wrapper setup don't clobber)

The code was trying to create solibbase symlink pointing to -> outbaselib, e.g.

    libdemo.so.1.0 -> build/lib.linux-x86_64-2.7/dsodemo/lib/libdemo.so.1.0

However if the source file in worktree already exists, symlinking was
failing with an error. Fix it by making sure that source file does not
exist before calling os.symlink.

Also there was related thinko in log.ingf describing who points to
who/where, which is corrected along the way.

Without the fix newly added test fails as

    ...
    running build_dso
    Building DSOs
    building 'dsodemo.lib.demo' DSO as build/lib.linux-x86_64-2.7/dsodemo/lib/libdemo.so.1.0
    creating build
    creating build/temp.linux-x86_64-2.7
    x86_64-linux-gnu-gcc -pthread -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fno-strict-aliasing -Wdate-time -D_FORTIFY_SOURCE=2 -g -fdebug-prefix-map=/build/python2.7-IbFBHb/python2.7-2.7.16=. -fstack-protector-strong -Wformat -Werror=format-security -fPIC -DBUILD_FOO -c foo.c -o build/temp.linux-x86_64-2.7/foo.o -DALL -DISC
    x86_64-linux-gnu-gcc -pthread -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fno-strict-aliasing -Wdate-time -D_FORTIFY_SOURCE=2 -g -fdebug-prefix-map=/build/python2.7-IbFBHb/python2.7-2.7.16=. -fstack-protector-strong -Wformat -Werror=format-security -fPIC -DBUILD_FOO -c bar.cpp -o build/temp.linux-x86_64-2.7/bar.o -DALL -DISCXX
    cc1plus: warning: command line option ‘-Wstrict-prototypes’ is valid for C/ObjC but not for C++
    creating build/lib.linux-x86_64-2.7
    creating build/lib.linux-x86_64-2.7/dsodemo
    creating build/lib.linux-x86_64-2.7/dsodemo/lib
    x86_64-linux-gnu-g++ -pthread -shared -Wl,-O1 -Wl,-Bsymbolic-functions -Wl,-z,relro -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -Wdate-time -D_FORTIFY_SOURCE=2 -g -fdebug-prefix-map=/build/python2.7-IbFBHb/python2.7-2.7.16=. -fstack-protector-strong -Wformat -Werror=format-security -Wl,-z,relro -Wdate-time -D_FORTIFY_SOURCE=2 -g -fdebug-prefix-map=/build/python2.7-IbFBHb/python2.7-2.7.16=. -fstack-protector-strong -Wformat -Werror=format-security build/temp.linux-x86_64-2.7/foo.o build/temp.linux-x86_64-2.7/bar.o -o build/lib.linux-x86_64-2.7/dsodemo/lib/libdemo.so.1.0 -Wl,-h,libdemo.so.1.0
    symlink libdemo.so.1.0 -> build/lib.linux-x86_64-2.7/dsodemo/lib/libdemo.so.1.0
    creating dsodemo/lib
    copying build/lib.linux-x86_64-2.7/dsodemo/lib/libdemo.so.1.0 -> dsodemo/lib
    copying build/lib.linux-x86_64-2.7/dsodemo/lib/libdemo.so -> dsodemo/lib
    running build_dso
    Building DSOs
    building 'dsodemo.lib.demo' DSO as build/lib.linux-x86_64-2.7/dsodemo/lib/libdemo.so.1.0
    x86_64-linux-gnu-gcc -pthread -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fno-strict-aliasing -Wdate-time -D_FORTIFY_SOURCE=2 -g -fdebug-prefix-map=/build/python2.7-IbFBHb/python2.7-2.7.16=. -fstack-protector-strong -Wformat -Werror=format-security -fPIC -DBUILD_FOO -c foo.c -o build/temp.linux-x86_64-2.7/foo.o -DALL -DISC
    x86_64-linux-gnu-gcc -pthread -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fno-strict-aliasing -Wdate-time -D_FORTIFY_SOURCE=2 -g -fdebug-prefix-map=/build/python2.7-IbFBHb/python2.7-2.7.16=. -fstack-protector-strong -Wformat -Werror=format-security -fPIC -DBUILD_FOO -c bar.cpp -o build/temp.linux-x86_64-2.7/bar.o -DALL -DISCXX
    cc1plus: warning: command line option ‘-Wstrict-prototypes’ is valid for C/ObjC but not for C++
    x86_64-linux-gnu-g++ -pthread -shared -Wl,-O1 -Wl,-Bsymbolic-functions -Wl,-z,relro -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -Wdate-time -D_FORTIFY_SOURCE=2 -g -fdebug-prefix-map=/build/python2.7-IbFBHb/python2.7-2.7.16=. -fstack-protector-strong -Wformat -Werror=format-security -Wl,-z,relro -Wdate-time -D_FORTIFY_SOURCE=2 -g -fdebug-prefix-map=/build/python2.7-IbFBHb/python2.7-2.7.16=. -fstack-protector-strong -Wformat -Werror=format-security build/temp.linux-x86_64-2.7/foo.o build/temp.linux-x86_64-2.7/bar.o -o build/lib.linux-x86_64-2.7/dsodemo/lib/libdemo.so.1.0 -Wl,-h,libdemo.so.1.0
    symlink libdemo.so.1.0 -> build/lib.linux-x86_64-2.7/dsodemo/lib/libdemo.so.1.0
    error: [Errno 17] File exists

It is used in several places and will be used more in the next patch.

build_dso for inplace mode copies DSO built in build/ into worktree.
However if the destination directory does not exist yet, copy_file
fails. Fix it by making sure before copying that destination directory
exits.

Without the fix added test fails as follows:

    ...
    creating build/lib.linux-x86_64-2.7
    creating build/lib.linux-x86_64-2.7/dsodemo
    creating build/lib.linux-x86_64-2.7/dsodemo/lib
    x86_64-linux-gnu-g++ -pthread -shared -Wl,-O1 -Wl,-Bsymbolic-functions -Wl,-z,relro -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -Wdate-time -D_FORTIFY_SOURCE=2 -g -fdebug-prefix-map=/build/python2.7-IbFBHb/python2.7-2.7.16=. -fstack-protector-strong -Wformat -Werror=format-security -Wl,-z,relro -Wdate-time -D_FORTIFY_SOURCE=2 -g -fdebug-prefix-map=/build/python2.7-IbFBHb/python2.7-2.7.16=. -fstack-protector-strong -Wformat -Werror=format-security build/temp.linux-x86_64-2.7/foo.o build/temp.linux-x86_64-2.7/bar.o -o build/lib.linux-x86_64-2.7/dsodemo/lib/libdemo.so.1.0 -Wl,-h,libdemo.so.1.0
    symlink libdemo.so.1.0 -> build/lib.linux-x86_64-2.7/dsodemo/lib/libdemo.so.1.0
    copying build/lib.linux-x86_64-2.7/dsodemo/lib/libdemo.so.1.0 -> dsodemo/lib
    error: [Errno 2] No such file or directory: 'dsodemo/lib/libdemo.so.1.0'

This covers .so files created with soversion, e.g. there can be
libdemo.so and libdemo.so.1.0 . The latter is covered by added patern.

No need to change dylib and dll patterns - according to current
setuptools_dso code, the soversion is either used before '.dylib'
suffix, or, for '.dll' case is not present in file name at all.

seems that some versions of GCC expand shell
variables in -Wl, which loses $ORIGIN

bdist_egg is a huge ugly hack!