Write processed suite.rc to suite dir.

Addresses #548; @dpmatthews and @steoxley - please review.

Note this writes out ```suite.rc.processed``` to the suite definition directory every time the suite is parsed, which includes validation and "cylc graph", etc., in addition to running and reloading the suite. It would be easy enough to restrict this to running and reloading as you suggested, but it's not entirely clear to me that that's the more desirable behaviour - any strong opinions?