hacks to work on osx with clang

Not sure if this is useful to others, but here's what I had to change in order to get gnuradio to build on osx. It wouldn't build with gcc42 or gcc44.

Summary of issues:

- Some member names in QT libs were referenced incorrectly (it seems QT may have renamed them at some point).
- Friend declaration can't provide default args (clang enforces this).
- `canvas()` returns parent class, need to upcast via `dynamic_cast` to correct qt type (I'm hardly a C++ expert so this could be completely the wrong thing to do)