Added check for activated advection flags

[arango]

I added a sanity check in the advection options for momentum and tracers in checkdefs.F. The model now will stop if the user defines more than one horizontal and vertical advection for momentum or tracers. Because of the way that advection is coded, the order of these options is important in the predictor and corrector algorithms. If you specify more than one option you will get a different behavior.

Many thanks to John Wilkin for pointing out this potential problem. Recall, that ROMS writes a lot of information to standard output. The users should pay a lot attention to the information that is written.