Use Thread.join() when halting the callback thread, rather than waiting for a threading.Event.
Added tests for escaped API communication
Fixes issue #31 on Google Code: parameter information for lowercase nd or is commands were not parsed.

Additional testcases for lowercase "is" and "nd" commands were added, and the response command string is forced to lowercase before being compared.

See http://code.google.com/p/python-xbee/issues/detail?id=31
Closes issue 35, as reported by Mark Fickett

Although all hardware ADC channels on an XBee ZB device are constrained to 10 bits
of precision across the range of 0v to 1.2v, when a supply volage threshold is set, an
XBee device may actually send a value beyond 10 bits of precision representing
the supply voltage.
Removes a no-longer relevant comment (oops).
If an empty frame is received from a device, it is ignored.
Merging github/blalor with googlecode repositories
Adding XBee wifi with NO TESTING yet
Adding XBee Wifi support with no testing code