branch boyceg: adding checks to ensure dt > 0 and integrator_time+dt <= end_time
branch boyceg: adding checks to ensure dt > 0 and integrator_time+dt <= end_time

huahbo/IBAMR,iamciera/IBAMR,yaojieuh/IBAMR,yaojieuh/IBAMR,huahbo/IBAMR,huahbo/IBAMR,yaojieuh/IBAMR,iamciera/IBAMR,huahbo/IBAMR,iamciera/IBAMR,yaojieuh/IBAMR,iamciera/IBAMR,yaojieuh/IBAMR,iamciera/IBAMR,huahbo/IBAMR,yaojieuh/IBAMR,iamciera/IBAMR,huahbo/IBAMR,yaojieuh/IBAMR,iamciera/IBAMR,huahbo/IBAMR