rt-inconsistency between one requirement and invariants are not reported / reported in the wrong part

[danieldietsch]

see #465

Ex. 3 is still broken.

req1: Globally, it is always the case that if "c" holds, then "a" holds after at most "50" time units
req2: Globally, it is always the case that if "c" holds, then "b" holds after at most "50" time units
req3: Globally, it is never the case that "a" holds.

Gives rt-inconsistency between req1 and req2; yet the conflict should be between req1 and req3 or at least just one.