Supplementary Services / Call Waiting in openbsc

Hi, I pushed the branches tobias/supplementary_services to libosmocore and openbsc repositories. The idea is to enhance openbsc to be able to provide Supplementary Services other than USSD. I tried to implement activation, deactivation and interrogation in a generic way. Registration is not yet implemented, also handling of different teleservices is missing (Everything will be treated as requested for "Telephony"). Call Waiting is now implemented on top of those changes (it is one of the SS that doesn't need registration). (De-)Activation and interrogation can be triggered from the phone using either the menu or the MMI codes *43#, #43# and *#43# (see GSM 02.30). So a call to a subscriber will now only proceed if said subscriber isn't busy or CW has been provisioned and activated. (For details see the commit messages.) I know this isn't the most sexy new feature, but I needed it to test something and maybe somebody wants to implement other supplementary services like call forwarding... -Tobias