Fix bugs in OpenCTM-Loader.

First: Error handling was not properly communicating failure to the
resource manager.
Second: Current stable FireFox release has two bugs that prevent the
WebWorker from transfering the OpenCTM ArrayBuffers to the main thread.
These bugs are fixed in version 27 (current Aurora channel).
We now branch if user agent sends browser FireFox with a version < 27
and copy the data instead.