Add paths to protocol buffer compiler/library/includes for mingw qmake build

I done did the following on the jenkins pull-tester machine:

1) chroot'ed to /mnt/chroot and apt-get installed libprotobuf-dev protobuf-compiler
2) Created /mnt/chroot/mnt/mingw/protobuf-2.5.0 with the right stuff in it (mingw-compiled .a, linux version 2.5.0 protoc, and all the src/)
3) Pulled this pull into /mnt/test-scripts/ 

Matt:  is /mnt/build-script* used for anything any more?