per the discussion at the triage meeting, we can count on the constraint eval function to use geval if and only when necessary, so we should be absolutely call positionConstriants, velocityConstraints, and stateConstraints on a manipulator without geval.

note: changed the default grad_method to 'user_then_taylorvar', which means that constraints must declare that they have gradient information to avoid hitting geval.  there might be some in the current examples that do not do this.
default constraint grad_method is ''
handle empty grad_method
Merge branch 'geval_constraints' of https://github.com/RussTedrake/drake into RussTedrake-geval_constraints

Conflicts:
	examples/RimlessWheel/runDircol.m
Merge branch 'RussTedrake-geval_constraints'