Several fixes and improvements for multi-dim fits

Hi Rene, This pull request makes a number of changes to make the cV-cF and rV-rF scans reproducible and tries to fix a couple of problems with the plotting. 

Felix: Can you check that none of these changes adversely affect the scans for the MSSM analysis? In particular that there are no problems with the plotting after the changes in src/MultidimFit.cc .  Let me know if there are and I will try something more robust.

cheers,
Andrew

 - Implement special combine options for --stable
 - Add instructions in sm-protocol for patching combine and running fits
 - Modify src/MultidimFit.cc to catch some cases where extra added points
   would have been in the wrong place
 - Updates to the plotting layout files