r 4258 in private: Check for defunct transactions when handling Paging Respone.

git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@4918 19bc5d8c-e614-43d4-8b26-e1612bc8e597
r4223 in Private: Clean up properly when we get the SIP 486 response.

git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@4919 19bc5d8c-e614-43d4-8b26-e1612bc8e597
Roughly r4224 in private:
More reliable detection of busy condition on MTC.
Also adds new GSM state, "Busy Reject".

git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@4920 19bc5d8c-e614-43d4-8b26-e1612bc8e597