Blender Git Loki

Another nuch of fixes/improvements to install_deps script, among which:
*New $INST variable to easily change the installation root dir of compiled libs.
*Better handling of versions for debian (DEB) too (and fix a bug for fedora (RPM) ones).
*Enhancements/fixes to compile_FOO funcs:
**Most notable, we now can force a recompile when we change something into these funcs, so user will always have latest-instructions compiled libs (else, he would have have to manually remove lib dirs under $INST...)
*General naming cleanup inside script (still wip).

Also adding boost date_time lib to linux in cmake file (why wasn't it there???).