time dependent forcing applied at incorrect time in timestep

_From @stephenprice on March 10, 2015 18:17_

In cism_driver/cism_front_end.F90, we have the option to read time dependent forcing fields from an input .nc file. Currently, we use this to read in an apply temperature, smb, and Dirichlet BC info (mask for where Dirichlet BCs are to be applied as well as the u and v vel fields to apply there). This capability is demonstrated in one supported test case (see ./tests/higher-order/dome/dome.forcing.*).

We found, however, that for implementing Dirichlet boundaries the u and v fields need to be applied at the **start** of the time step, whereas the smb and temperature should be applied at the **end** of the time step. The current implementation only allows for one choice (all fields are read in and applied at the same time).

Right now, the problems that arise from this inconsistency are worse if we leave the forcing at the end of the time step as opposed to moving it to the start of the time step (we can't make progress on simulations with time dependent vel BCs applied, a priority for validation), so we will move it to the start. Thus, the smb and sfc air temps are being applied as bcs / source terms at the wrong part of the time step. This can / should eventually be fixed by allowing for different forcing fields to be applied at different parts of the time step.

_Copied from original issue: E3SM-Project/cism-piscees#19_