throw error when assigning bounds to non-existent parameters

See http://openmx.psyc.virginia.edu/thread/450

Fixed in r1179. Added test case models/passing/MxBoundsTesting.R

This sounds ok but could be tricky because of possible inconvenient side-effects. It might be a case where a warning would be better, but let's wait and see.

Automatically closed -- issue fixed for 2 weeks with no activity.