documentation clarification on exclusive node groups
added test for recently fixed crctx bug of duplicate commods
test for incorrect map iteration bug in ApplyThreshold
Merge pull request #814 from rwcarlsen/bugs-fix

add tests for bugs fixed in #811
check for NULL parent before calling agent's parent's DecomNotify
fixed next ids not being loaded properly. changed model destructor to not destruct children - causing segfaults due to improper unregistration for time and dre listening