Make wide char versions of opendir and friends.
* include/dirent.h (_wdirent, _WDIR): Define wide versions of
struct dirent, DIR.
(_wopendir,_wreaddir,_wclosedir,_wrewinddir,_wtelldir,
_wseekdir): Add prototypes for wide versions of corresponding
standard functions.
* include/tchar.h; Add _UNICODE mappings for dirent.h
structures and functions.
* mingwex/dirent.c: Make _UNICODE neutral.
* mingwex/wdirent.c: New file to define _UNICODE before
including dirent.c.
* mingwex/Makefile.in (DISTFILES): Add wdirent.c/
(POSIX_OBJS): Add wdirent.o.
(wdirent.o): Specify dependency on dirent.c as well as
wdirent.c.
* samples/dirent/wtest.c: New file, wide version of test.c.