Added global config parameter: 'transfer_on_hangup' (default=off), which will complete transfer, when the transferer hangups up, after the destination has been reached. Making a second press of the transfer button unnecessary. However this does make cancelling a transfer a little harder, either press resume on the transfered channel or have the receiving party hangup first (might be considered a negative side effect, there for 'transfer_on_hangup' is switched 'off' by default).

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@4729 43c1dc8c-776e-4df2-8ef1-6e829299be21