accessor for g_GIT_SHA
pdal app needs PDAL object target
use StageFactory to create readers
use accessor to get SHA1
fix plugin tests to use Stage creators
Merge remote-tracking branch 'origin/windows-gitsha-access' into hobu-windows-rollup
Merge branch 'hobu-windows-rollup' of https://github.com/PDAL/PDAL into hobu-windows-rollup
test fixups