Return Requests Must Be --force 'd

[blinkdog]

The size check in lta_cmd.py will stop return requests (NERSC -> WIPAC) from being created.

The flag --force can override this safety check, but it will ALSO override the check for duplicate requests (if the path matches a request already in the system).

Probably want to:

• Make sure the size check only runs when the source is WIPAC
• Split the --force flag into --zero-size-ok and --duplicate-request-ok so we can be sure the operator's intent is clear.