With --force (-f), rm no longer fails for ENOTDIR.

With --force (-f), rm no longer fails for ENOTDIR.
* src/remove.c (ignorable_missing): New function.
Use it everywhere, rather than open-coding the test.
Andreas Schwab reported the ENOTDIR problem.
(ignorable_missing): Similarly, don't fail for ENAMETOOLONG.
* NEWS: Mention the bug fix.
* tests/rm/ignorable: New file.  Test for the ENOTDIR case.
* tests/rm/ignore-name-too-long: New file. Test for ENAMETOOLONG.
* tests/rm/Makefile.am (TESTS): Add the new file names.