rework the MSVC version logic slightly, add possibility of VC2012/2013 to pdal_defines
Merge pull request #398 from chambbj/issues/397-msvc-version-handling

rework the MSVC version logic slightly, add possibility of VC2012/2013 to pdal_defines

Closes #397
Sbet reader to point context.
Merge branch 'master' of https://github.com/PDAL/PDAL into point-context