Pre-RFC: CAmkES pre_init() and pre_post() need a return code

The CAmkES function pre_init() and pre_post() need a return code, so any initialization error can be reported back to the CAmkES runtime. The runtime shall then stop any further activities like calling post_init() or enabling RPC handlers - and also guarantee this.
We are running in situation, where code in either pre_init() or post_init() can fail and there is not really a nice way to deal with this. Calling some abort() might also solve this, but that would still require implementing this everywhere. Just returning FALSE (or an error code) keeps any details internal to the CAmkES runtime, so this can be changed later to whatever mechanism is implemented. Halting the system seems the obvious choice for now, as there is no recovery and a failure in initialization some likely some some broken configuration.