add timestamp to rpointer files

[jedwards4b]

Add timestamps to rpointer files, initialize curr date from driver and compare to what is in the restart files (instead of initializing from restart files).

[wwieder]

I see this is no longer a draft. Are you ready for a review, Jim?

[jedwards4b]

@wwieder Note that this is for mosart and is ready for review. I will update the clm PR tomorrow.

[wwieder]

Thanks for making the mosart PR. What's the priority and timing of this across CESM?

[jedwards4b]

I would like this to go into the cesm3_0_beta04 tag - probably within 30-45 days.