Improvements to avgSupplyJet.
Improvements to avgSupplyJet.

1. Do a calculation for unmasked velocity field on the shelf — no
partitioning. Estimate a Gaussian decay scale for this.

2. supply.shelf has similar diagnostic but now for /only/ shelf-water.

3. The intersection of the unmasked and masked vertically-integrated
velocities tells me where the supply is all shelf water.

4. Note that all the velocity on the shelf is -ve in the time mean
because of how the leakage is basically a gravity current.
So, I remove the (asvel < 0) filter.

dcherian/eddyshelf,dcherian/eddyshelf,dcherian/eddyshelf