(bug 37331) Modules sometimes execute twice in Firefox

(bug 37331) Modules sometimes execute twice in Firefox

This seems to have been caused by a weird race condition that caused the
loader to run while the module in question was also running; could also
have been caused by the module calling mw.loader, but that didn't seem
to be the case here.

The fix is to set .state='ready' before executing the module rather than
after. We can't do this in debug mode (where we're loading raw files and
can't execute things at will), but we have to do this in production
mode to prevent these freakish double executions.

Change-Id: I7e8dbd361fb265e520d3935e3a1fc7e3b6710b66