Port GEM software from 62XSLHC to 72X

Hi,

As a first step to port the GEM software from 62XSLHC to 72X I started from (*) and listed all geometry-related commits. I ignored all non-GEM commits and commits that were simply merges. I solved most conflicts manually. The resulting code compiles, but I have not been able to test it yet. Which workflow can I use to test it?

EDIT: fixed various suggestions by Slava
EDIT2: include the frame rotation fixes in SimG4CMS/Muon
EDIT3: include ME0DigiPreReco dataformat from DataFormats/GEMDigi

Cheers,
Sven

(*)
<PRE>
commits=( $(git log --topo-order official-cmssw/CMSSW_6_2_X..official-cmssw/CMSSW_6_2_X_SLHC --reverse --pretty=format:%h -- Geometry/GEMGeometry Geometry/GEMGeometryBuilder Geometry/GlobalTrackingGeometryBuilder Geometry/CommonDetUnit Geometry/Records DataFormats/MuonDetId Geometry/MuonNumbering CondTools/Geometry) )</PRE>