quartz/x11 conflict

[Ludwig]

I uninstalled everything gtk2 related all the way down to cairo in an
effort to get gtk2 +quartz installed.  Yet when installing gtk2
+quartz
directly, in installs pango and cairo +quartz+x11, which causes gtk2 +quartz
(which conflicts with +x11) to fail, as it requires pango to be built
-x11.  Okay,
fine, manually install pango +quartz +no_x11.  Oops, that requires
cairo to be
built -x11.  Build that by itself.  Then build pango by itself.  Then
gtk2.
That seems to work.

But seeing as how +x11 and +quartz are incompatible at such a low
level, shouldn't
they be mutually exclusive in all dependent ports?