* src/inp.c (get_input_file), src/pch.c (there_is_another_patch,
intuit_diff_type): Use lstat instead of stat. This causes patch to
refuse patching symlinks (get_input_file() will refuse to read them).
* src/util.c (create_backup): Refuse to create backups of symlinks.
* tests/symlinks: New test case.
* tests/Makefile.am (TESTS): Add test case.
* bootstrap.conf: Use the gnulib lstat module.