qgis-24: clean up formula; remove skip-stdlib-check option
qgis-24: fix Qsci header path
qgis-24: update .app bundle identifier regardless of build type
qgis-24: if Homebrew Python, make sure its found first
qgis-24: ensure CMake bool options always match formula's install options
qgis-24: fix PYTHONHOME; set install's site-packages first
qgis-24: patch backports and bump revision to 2