Fix overzealous patterns in .hgignore, which used to hide files containing e.g. "python".

(also an occasional source of bugs on the hgsvn-generated hg mirrors)

.hgignore

 .gdb_history
 .purify
-.svn
+.svn/
 Makefile$
 Makefile.pre$
-TAGS
-autom4te.cache
-build
-buildno
+TAGS$
+autom4te.cache$
+build/
+buildno$
 config.cache
 config.log
 config.status
 config.status.lineno
 db_home
-platform
-pyconfig.h
-python
-python.exe
-reflog.txt
-tags
+platform$
+pyconfig.h$
+python$
+python.exe$
+reflog.txt$
+tags$
 Lib/plat-mac/errors.rsrc.df.rsrc
 Doc/tools/sphinx/
 Doc/tools/docutils/
 Doc/tools/jinja/
 Doc/tools/pygments/
 Misc/python.pc
-Modules/Setup
+Modules/Setup$
 Modules/Setup.config
 Modules/Setup.local
 Modules/config.c
-Parser/pgen
-core
-python-gdb.py
+Parser/pgen$
+^core
+^python-gdb.py
 
 syntax: glob
 libpython*.a