enable .gsutil_is_uri checks for destination inputs in gsutil cp

[LiNk-NY]

.gsutil_requesterpays_flag interface allows for destination inputs with a default of ""

• run requesterpays get separately for both source and destination
• addresses can gsutil_cp use the project id for requester pays buckets? #82

[mtmorgan]

OK; since I guess this is relatively 'expensive' does it make sense for gsutil_requesterpays() to return scalar TRUE if any location is requester pays, and implement this as a loop that exits on first detection of requester pays?

[LiNk-NY]

Thanks Martin @mtmorgan
I've made the change to loop through the buckets and break when requester pays is enabled in one of them.