recipes for Qt5/sip/PyQt5 stack on windows, linux, osx

Compiles Qt5, sip, and pyqt5 using MSVC Express (tested with 2008 for py27, 2010 for py3k). Uses precompiled ICU binaries (build and runtime requirement for Qt5 on windows), and uses precompiled jom executable to perform the build in parallel.

Qt5 is given a python requirement to differentiate qt5 built with msvc2008 for py27 and qt5 built with msvc2010 for py3k. Linking pyqt5 built with msvc2008 to a qt5 built with msvc2010 resulted in crashes in a few of PyQt5's examples, notably qtdemo.py
Actually, quoting these variables causes the qmake build (the first step of the build process) to fail. It looks like it will be necessary to document that qt5 can't be built on systems where the _build environment or conda-bld directories have spaces in their paths. I doubt many people with spaces in their home directory path are going to be interested in trying to actually build this conda package.