update register command to work with linphone 3.6
prevent IPC semaphore leaks using 'quit' command

linphone doesn't clean up its IPC semaphores when it's
stopped abruptly using SIGKILL. (can be seen with ipcs).
So instead of stopping the process with pexpect.terminate(),
we send the 'quit' command, giving linphone a chance to
terminate by itself cleanly.
fix unittests
add test when process is still alive after quit command
exceptions generated in __del__ are never raised
Merge pull request #1 from xivo-pbx/linphone_3_6

Linphone 3 6