Fix for issue #523: upstream project dependencies

- GDAL is a required library now; all code that was conditional under PDAL_HAVE_GDAL is now unconditional; macro removed

- all code conditional under PDAL_SRS_ENABLED is now unconditional; macro removed

- Crop filter throws if non-empty poly and GEOS not built in

- geotiff not required now

- some SRS tests in SpatialReference and ReprojectionFilterTests now under #Ifdef GEOS -- *needs to be checked, @abellgithub said he'd look*

- ZLIB always required now

- XML2 will be enabled now if a DB is enabled (cmake-only fix)

- MSGPACK removed entirely from cake

- DEMANGLE code changed to a single #ifdef windows in Utils.cpp