Use typedefs judiciously in ConstraintWarehouse.C

I definitely realize that going crazy with typedefs is a bad thing,
but in this particular case I think it makes the code more readable
for humans.

Refs #3692.
Merge pull request #4359 from jwpeterson/use_typedefs

Use typedefs judiciously in ConstraintWarehouse.C
Merge commit 'ab58360f3ce96a0cd6d911f4e8f57f938cbf2e91'