xproto changes from NetBSD xsrc and pkgsrc

[Thomas Klausner]

The pkgsrc package has attracted quite a number of patches.
This is a try getting them included.

Additionally, I wonder if this _POSIX_SOURCE dance for limits.h is
still useful (in Xos_r.h):

# ifndef X_NOT_POSIX
#  ifdef _POSIX_SOURCE
#   include <limits.h>
#  else
#   define _POSIX_SOURCE
#   include <limits.h>
#   undef _POSIX_SOURCE
#  endif

Comments welcome!