Add --without-isam configure switch.

Portability fix for mysqlmanager.


acconfig.h:
  Add HAVE_ISAM
acinclude.m4:
  Add --without-isam configure switch.
configure.in:
  Add --without-isam configure switch.
include/my_global.h:
  remove #define HAVE_ISAM
libmysqld/examples/test-run:
  pass --language option to embedded server
sql/Makefile.am:
  use @isam_libs@ instead of hard-coded values
tools/mysqlmanager.c:
  #include <signal.h> for portability