groups simultaneous requests to the same resource
just use outstandingRequests instead of new obj
use a clone of resp for each handler
only clone response if is object
Merge pull request #3877 from seanmonstar/simultaneous-requests

groups simultaneous requests to the same resource

Only one call to `/wsapi/session_context` in the dialog. IE10 is happy. IE8 is happy. Tests all pass, backend, frontend, Selenium. Nice work @seanmonstar!

r+