Merge known-project lists from multiple processes

Solution for issue #506 

This fix should be of interest to anyone who uses more than one Emacs instance at a time. 

hmm, there is a subtle two differences in what it achieved. The two that are exactly alike are on the load and save functions which are located in the same place in the file.. I feel that it makes sense to keep them where they are.. I am currently making small changes to the docstrings and such and will soon update the pull request.