make pexpect run linphone in background

reason: linphone needs to handle spontaneous network messages, even
when pexpect is not requiring any output. Plus, linphone may need to
send SIP message after outputting the expected message.
set RTP port when creating session

reason: running multiple Linphones on the same machine need to use
different SIP and RTP ports
remove config file after linphone terminates

reason: linphone writes its config into the config file when it stops,
thus recreating the file previously removed
add new status for phone
quick hack to make linphone 3.7 work