fixed remaining Slot/iotype issues. Switched Deprecatin to FutureWarning. Fixed documentation.
Update variables.rst

Fixed typo on line 548 (tow -> two).
Merge pull request #1584 from crobinsonut/dev

switched DeprecationWarning to FutureWarning
Merge branch 'bench' of github.com:Kenneth-T-Moore/OpenMDAO-Framework into bench
working