This commit includes:
1. Consolidate functions into appropriate modules
2. Rename modules to reflect contents (v4l2, bktr, common)
3. Combines v4l2 and bktr so they can be used together
4. Implements functional prefixes
5. Uses HAVE_V4L2, HAVE_BKTR instead of WITHOUT_
6. Include pthread_np.h for FreeBSD
