Added invoke_when_ready utility
Added support for futures as arguments to remote actions
Added future get_exception_ptr
Fixing gcc 4.4 compilation error
Tests for using futures as arguments to actions
Moved invoke_when_ready to a detail namespace
Refactored invoke_when_ready callback to be its shared state
Merge pull request #1128 from STEllAR-GROUP/action_future_args

Action future args