Bugfix: Incorrect hardcoded z position of plane 0 in TSolSimDecoder
Straighten out the generation of back tracks in the decoder

The original code was a veritable mess because back tracks originally
included all apparent tracks, not just the ones from the primary signal
particle.
Add "ufail" and "vfail" variables to TSolSimBackTrack

These allow determining the per-plane, per-readout digitization
efficiency at a single glance.
First shot at an API for retrieving MC truth data for digitized hw channels

In reality, this will require a generic SimDecoder base class to be
added to the analyzer.
Make TSolSimDecoder a derived class of Podd::SimDecoder

This uses the new simulation decoder interface in Podd. Requires
at least Podd version 1.5.27.
Remove hardcoded z-pos of 1st tracker plane in Decoder, make it configurable
Let TSolSimDecoder populate the new fMCPoints array in SimDecoder
Do not use operator= to copy the tracks TClonesArray in TSolSimDecoder

TClonesArray::operator= is apparently very inefficient.

This could be made even more efficient if our global variable system
supported dynamically changing pointers to TClonesArrays. Then we
could just assign fMCTracks the pointer to the TClonesArray in
TSolSimEvent.
Record one track point per projection in TSolSimDecoder

The generic track point class MCTrackPoint implicitly assumes that each
tracker plane corresponds to a measurement of one coordinate axis only.
For GEMs, two such "planes" (=2D readout) simply happen to be at the same z.
Update global variables in TSolSimDecoder

- Add forgotten "hit.src" (apparently overlooked when moving to github
  since I have it in my Sep 22, 2013 source code)
- Remove "btr.src" since back tracks are by (current) definition always
  from source 0 (signal)
- Add cylindrical/spherical representation of hit coordinates
- Update variable descriptions
Update TSolSimDecoder for new MCTrackPoint constructor. Set fMCTime.
Update DefineVariables to pick up MCTrackPoint info from latest SimDecoder
Make plane number in MCTrackPoints consistent with GEMCluster
Calculate plane-to-plane difference quantities (eloss etc.) for MCTrackPoints
Compile production version with -O2 -DNDEBUG. Link correct EVIO debug libs.
Fix buggy calculation of plane-to-plane MCTrackPoint differences