Initial round of fixes to based on Paul's W13 review.
Addressed all ticket comments from Paul and Serge.  Will build and run unit tests next.
Moving calculation of Psf FWHM into subroutine, and background subtraction into a try block, to address more #2822 comments
Refactored the code to add fields to the schema to iterate over a dictionary instead of explicitly assingning a field object for each metric name
Edited line to not run over 100 characters, also white space changes (sorry Paul)
Additional whitespace changes to KernelCandidate.cc as suggestedin #2822
Fixing missing commas in psfMatch
Modifications to unit test ImagePsfMatch, fixing bugs in teh background subtraction of templates and type checking in getSelectSources, for the candidate list in makeCandidateList
Removing AfwBackgroundConfig from unit test, the code now uses an actual afw BackgroundConfig instance.
Fixing broken unit tests when afwdata is set up
Final changes to code base to get imageDifferenceWinter2013.py to run end-to-end.
adapt to changes in meas_deblender names
Merge branch 'tickets/3112'
Merge branch 'tickets/2822'
Merge remote-tracking branch 'LSST/master'