#987 OBForceField functions ignore convergence criteria

[Michael Kausch]

When doing a force field minimization of a molecule with Open Babel 2.4.1 the optimization continues till the completion of number of steps specified. A convergence criteria given is ignored.
Reason is that the OBForceField functions e.g. ConjugateGradientsTakeNSteps, SteepestDescentTakeNSteps, SteepestDescent etc. all do not return FALSE (or return) if convergence criterion has been reached.
The parameter econv seems to be ignored in all functions.

Tested with Openbabel 2.4.1 (64bit) and Win10 pro 64 bit.
This bug was not present in Open Babel 2.3.2.

see also:
https://sourceforge.net/p/openbabel/mailman/message/35400728/