Qt5 static osx linux

From the main commit:
This is the first part of a huge effort to rework the handling of dependencies. To start, this change allows all supported platforms to build against a static Qt. 5.2.1 and 5.3 have been successfully tested against osx64, win32, win64, linux32, and linux64.

It also makes a small change to the windows config, to allow linking against qt builds with or without built-in libjpeg/libpng/libpcre/libz.

The actual build processes to take advantage of these changes (for gitian and pull-tester) are forthcoming. Until then, this should be a no-op.