Move an import statement to top of file.

[e000]

On twisted.internet.task, we should move

    from twisted.internet import reactor

to the top of task.py

(_defaultScheduler, line 305)

[exarkun]

Importing the reactor has an unfortunate side-effect. If no reactor exists yet, then the default reactor is instantiated and installed. For this reason, modules in Twisted try to avoid importing the reactor as a side-effect of being imported themselves. Thus the reactor import hidden inside the _defaultScheduler function.