This makes the system package fully nixified in the sense that
for i in $(nix -qn $(fix system/system-template-everything.fix))/bin/*; \
do echo $i; ldd $i; done
shows that the programs in the system package only link against libraries in
the Nix store.
(Some builders still use header files from /usr/X11/include, though.)
svn path=/nixpkgs/trunk/; revision=376