gdb/Changelog:
* objfiles.c (objfile_filename): New function.
* objfiles.h (objfile_filename): Declare it.
(objfile_name): Add function comment.
* python/py-objfile.c (objfpy_lookup_objfile_by_name): Try both the
bfd file name (which may be realpath'd), and the original name.
gdb/testsuite/ChangeLog:
* gdb.python/py-objfile.exp: Test gdb.lookup_objfile on symlinked
binary.