Fix documentation issues for restricted bending potential#
The actual implementation in the code was correct, but the manual section for the restricted bending potential had an extra factor 2 for the force inherited from the 2013 Bulacu JCTC paper, and the journals for two of the references had been swapped. No changes to any simulation results.
gmx grompp -maxwarn to take a positive integer#
Previously -1 was accepted and suppressed all warnings. Now a positive integer must be chosen.