selfupdate with GNUstep

[Anders F Björklund]

When using "port selfupdate" on platforms other than Mac OS X
(such as Darwin, FreeBSD, Linux and probably most others too)
it fails to find Foundation unless you set the environment up:

checking for Apple Objective-C runtime... no
checking for GNU Objective C runtime... yes
configure: Using GNU Objective-C runtime
checking for Apple Foundation library... no
configure: WARNING: GNUSTEP_SYSTEM_ROOT is not defined in your 
environment, preventing the use of GNUstep's Foundation library
configure: error: Could not find a working Foundation implementation

Can we source 
{/usr,/usr/local}/GNUstep/System/Library/Makefiles/GNUstep.sh,
as part of the "selfupdate" target, so that it works without 
configuration ?
("gnustep-base" is required to provide Foundation, for the tclobjc1.0 
module)

--anders

PS. Ironically enough, GNUstep is not support on Darwin OS...
But it works out of the box on FreeBSD and most Linux distros.
For now I just set it up as part of the MP installation package.