make the crop filter a builtin filter once again
_VARIADIC_MAX must be increased on msvc for gtest
Merge pull request #651 from PDAL/gtest-fix-msvc

_VARIADIC_MAX must be increased on msvc for gtest
Merge pull request #650 from PDAL/make-crop-builtin-filter

make the crop filter a builtin filter once again
Use OPTIONAL_COMPONENT_SWITCH for attribute plugin

Best to test with and without on Travis.