Explicitly cast CollectionPtr
UnitTestReadWriteMeshJSON.cxx will not compile on Ubuntu 14.04 (gcc 4.8.4), because gcc cannot implicitly cast CollectionPtr to an integer. This mod fixes that by comparing the CollectionPtr to a null pointer (to get a boolean which the compiler can cast to an int). FYI the error message is pasted below.
/media/ssd/sim/cmb_core/gitlab/SMTK/smtk/mesh/testing/cxx/UnitTestReadWriteMeshJSON.cxx: In function ‘void {anonymous}::verify_writing_and_loading_collection()’:
/media/ssd/sim/cmb_core/gitlab/SMTK/smtk/mesh/testing/cxx/UnitTestReadWriteMeshJSON.cxx:107:67: error: cannot convert ‘smtk::mesh::CollectionPtr {aka std::tr1::shared_ptr<smtk::mesh::Collection>}’ to ‘int’ for argument ‘1’ to ‘int test(int, const string&)’
"Collection UUID can't change when being loaded from JSON");