- Made framework builds work for MacOSX. The configure arg is now
  "--enable-framework".
- Added an install target frameworkinstall which installs the framework.
- Ripped out Next/OpenStep support, which was broken anyway.
- Made the MacOSX toolbox glue dependant on a --enable-toolbox-glue
  configure arg. This should make naked darwin build work again (untested).

A few targets have been added to Makefile.pre.in, and on inspection they
look harmless to non-MacOSX machines, but it is worth checking.

Closes bug #420601 and patch #450350.