New module 'iswctype'.

New module 'iswctype'.

* modules/iswctype: New file.
* lib/wctype.in.h (iswctype): New declaration.
* lib/iswctype.c: New file.
* lib/iswctype-impl.h: New file.
* m4/iswctype.m4: New file.
* m4/wctype_h.m4 (gl_WCTYPE_H): Test whether iswctype is declared.
(gl_WCTYPE_H_DEFAULTS): Initialize GNULIB_ISWCTYPE.
* modules/wctype-h (Makefile.am): Substitute GNULIB_ISWCTYPE.
* tests/test-wctype-h-c++.cc: Test the declaration of iswctype.
* doc/posix-functions/iswctype.texi: Mention the new module and the
HP-UX 11.00 problem.