Title: Fixed possible exceptions of CMC Check_MK helpers when using some custom checks
Level: 1
Component: checks
Class: fix
Compatible: compat
State: unknown
Version: 1.2.7i1
Date: 1421918120

When using the CMC together with some custom checks which register variables
in the global context which can not be written out with repr() and read with
eval() like for example python module references or function pointers, all
Check_MK workers stopped working and were restarting in an endless loop.

A verification has been added to prevent those variable from being written
to the Check_MK check helper config var/check_mk/core/config.mk.
