test-fopen-safer: split from test-fopen * tests/test-fopen.c (main): Move... * tests/test-fopen.h: ...into new file. * tests/test-fopen-safer.c: New file. * modules/fopen-tests (Files): Add test-fopen.h. * modules/fopen-safer-tests: New file. Suggested by Bruno Haible. Signed-off-by: Eric Blake <ebb9@byu.net>