Update MacOS X dependency build.

- use $NUMCPU for parallel build
- don't always rebuild libs when already installed
- switch to Qt 5.3.1 and disable most modules
- switch to eigen 3.2.1
- fix build order for ragel (needed by harfbuzz build)
Merge pull request #897 from openscad/macosx-build-fix

Update MacOS X dependency build.