Added streams freeing in VSGPUManager.
Began stream reorganization work. Not complete and untested.
Improved stream wrapping, compiles, but not complete.
Reworked vsgpumanager to fix a crash on exit.

Freed streams array as well.
Add important comment about code from previous commit.
Fixed a crash in previous commit and improved resource handling.

Also, renabled external plugin building again! Can finally
build plugins without importing CUDA headers due to the new
VSCUDAStream struct.
Merge branch 'stream_wrapper' into cuda

Conflicts:
	src/core/vsgpumanager.cu