First good version of the script to test release-candidates.

This pull request introduces robotpkg-test-rc.py to compile several packages from robotpkg with different branches. Everything starts from robotpkg deployed in: ~/devel-src/robotpkg-test-rc/robotpkg ~/devel-src/robotpkg-test-rc/install All the others packages are compiled from release. The python file handle its own environment in order to avoid any mix with another installation.