Please review and test zecke/channel-release

Hi, I have rebased, extended and fixed the channel assignment and release. It brings us closer to the GSM 04.08 specification but there are still sime minor violations for the abnormal handling. I have tested (using the FakeBTS) a phone not acting on the SACCH deactivate/RF Channel Release and the signalling link will be released (T3109). I have a manual SMS submit test and I can make the nanoBTS crash easily. I have rebased through each individual change and couldn't reproduce the crash. I think it is either something in the RF setup (the modem bank being too close to the BTS), the older modem firmware, etc. Anyway, please review and test the branch. I plan to merge it by Wednesday. thanks holger