HAVE_PWD_H

[David Robinow]

Recent changes to fileio.c, editfns.c, etc. have broken the MS Windows
build.  Although nt/inc/pwd.h exists, configure.bat does not detect
it.
HAVE_PWD_H, of course, can be unconditionally defined but I'm not
sure exactly where to do it so I'm not including a patch.
 However, conditionalizing the   #include <pwd.h> doesn't seem right
to me, unless the use of  "struct passwd" is also conditionalized.  As
it is now, if pwd.h is not included, the code won't compile.