main client's close function

[CurleySamuel]

Right now it shuts down all region clients immediately without letting them send off their outstanding RPCs.

We have a few handling options -

1. Make close let all outstanding RPCs send before closing region clients and thus returning.
2. Do the above but make close asynchronous (function call returns immediately but continues closing the client in the background)
3. Leave close how it is, effectively operating as a 'force close'.
4. Provide two different close functions. One that's asynchronous and lets all outstanding messages send/receive before closing and one that'll force close the client.

thoughts?