Future: tryUnwrap to prefer universal references
Future: tryUnwrap to prefer universal references

With a const reference, it would potentially call implicitly for a
constructor of qi::Future which may wait for the value to be returned.

Change-Id: I9524774455f386ab7cf3a613e2cfdefb472f6161
Reviewed-on: http://gerrit.aldebaran.lan/69600
Reviewed-by: jlamotte <70353e7b0c7d18b7fc75605daf0ccba69fcd3222@aldebaran.com>
Tested-by: jmartin <922bc0e434646289e9f50fcc60c6e6c35f200683@aldebaran-robotics.com>

aldebaran/libqi,aldebaran/libqi,aldebaran/libqi