No more x11prefix

[Jeremy Huddleston]

I just pushed the patch I submitted two days ago and a follwup patch  
to base that removes its search for a system X11 SDK at build time and  
all references to x11prefix.

At this point, no ports in MP should be referencing /usr/X11 in any  
way.  If you discover a port that is linking against /usr/X11/lib/...,  
please let me or the maintainer of the port know.  The most likely  
cause is that it's an autoconf package that is using AC_PATH_X to find  
X11 (poke upstream to use pkg-config first, then fall back on  
AC_PATH_X).

Older versions of AC_PATH_X didn't know about the .dylib extension for  
libraries.  Furthermore, AC_PATH_X defaults to "asking" xmkmf  
(port:imake) for the location of X11 headers and libraries if it's  
available.  Now that $x11prefix/bin is not in base's build $PATH  
(granted it will take a while to reach users), this is less of a  
problem (although port:imake needs to be updated since it seems to be  
reporting /usr/X11 too...)

The easiest solution to this right now is to just add the following to  
configure.args for ports that misbehave:
--x-include=${prefix}/include --x-lib=${prefix}/lib

Most ports that use AC_PATH_X will probably build and link correctly  
even if they find /usr/X11 because $prefix should be before it on the  
command line.

--Jeremy