Since we are moving towards only depending on X11 for X-headers, superenv now doesn't automatically add X11 compilation. I was reluctant to do this, but it is the right thing to do now that X11 is not automatically installed by OS X or Xcode.
I didn't implement ENV.x11 because the order that the X headers are inserted is important. It must be done at initial setup to ensure that brewed versions of e.g. freetype and Cairo are used and not the ones installed by XQuartz.
1. A minimal build environment, we don't set CFLAGS, CPPFLAGS, LDFLAGS, etc. the rationale being, the less that is set, the less variables we are introducing that can break builds.
2. A set of scripts that replace cc, ld, etc. and inject the -I, -L, etc. flags we need into the args passed to the build-tools.
Because we now have complete control over compiler instantiations we do a variety of clean-up tasks, like removing bad flags, enforcing universal builds and ensuring makefiles don't try to change the order of library and include paths from ones that work to ones that don't.
The previous ENV-system is still available when --env=std is specified.
superenv applies to Xcode >= 4.3 only currently.
