Recognize more residue labels as water in the Amber file parser.

At some point, at least, TP4 was the residue label for water (I think tleap
currently translates most of the water residue labels to WAT, but there are at
least some -- like $AMBERHOME/test/tip4p/prmtop -- that use older labels).

wrappers/python/simtk/openmm/app/internal/amber_file_parser.py

@@ -720,7 +720,7 @@ def readAmberSystem(prmtop_filename=None, prmtop_loader=None, shake=None, gbmode
         system.addParticle(mass)
 
     # Add constraints.
-    isWater = [prmtop.getResidueLabel(i) == 'WAT' for i in range(prmtop.getNumAtoms())]
+    isWater = [prmtop.getResidueLabel(i) == ('WAT', 'TP4', 'TP5', 'SPF', 'SPG') for i in range(prmtop.getNumAtoms())]
     if shake in ('h-bonds', 'all-bonds', 'h-angles'):
         for (iAtom, jAtom, k, rMin) in prmtop.getBondsWithH():
             system.addConstraint(iAtom, jAtom, rMin)