unittest for htsp python library + additional methods

Hi

I wrote a basic unittest for the htsp python library, and added some methods and argument checking to the library.  (Arg checking is unpythonic normally, but makes sense when it is an interface)

Please excuse me if I have not followed the github/pull process correctly, but this is my first use of this stuff.  Thanks for TVheadend - it works great.



Added unit test script for htsp.py to htsp_test.py.  Can be run with -v ......for verbose listings.

Added number of additional client-server methods to htsp.py
Added argument checking to htsp.py using assert (which can be ignored when run optimised)