Bug 986582 - Get rid of the toolkit.telemetry.enabledPreRelease pref and make the toolkit.telemetry.enabled pref do the right thing for beta users who are testing a final release build, r=rnewman

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extra : rebase_source : 43f70e2c1c3207f37ba0789245958cb0c34187f6
Bug 985089 followup: fix mis-spelling of isNaN, r=gfritzsche