This incorporates:
2015-03-19 fdopendir: port better to MinGW
2015-03-18 fdopendir: fix typo in comment
2015-02-24 glob, etc.: port to MSVC v18 on MS-Windows 8.1
* lib/dirent.in.h, lib/fdopendir.c: Update from gnulib.
* lib/dirfd.c, m4/dirfd.m4: New files from gnulib.
* lib/gnulib.mk, m4/gnulib-comp.m4: Regenerate.
