cfgutils: init probability pointer to NULL

- otherwise it can be an attempt to free it when the kamailio does not
  start due to config errors
- reported by Dragos Oancea
mohqueue: fixes

* cleaned up all error paths (fixed crashes)
* added support for INVITEs that get stuck
* adjusted code to avoid compiler warnings
* PRACK only invoked if Require: 100rel set
* fixed bug that allowed a new call to be created more than once

Documentation
* updated NOTES
modules/ims_charging: corrected default termination cause code to DIAMETER_LOGOUT
	- also corrected typo
	- added other termination cause code defines for future use
Merge branch 'master' of ssh://git.sip-router.org/sip-router
modules/ims_charging: fixed bug not initialise AVP string value for success CCA
modules/ims_charging: restored an unlock that will cause deadlock if omitted
ims_charging: Merge branch 'ims_charging' into master