terminal_input.js:  Fixed a bug in disableCapture() where metaHeld was being set incorrectly (was setting GateOne.Terminal.Input.metaHeld instead of GateOne.Input.metaHeld which is the right place for that).
gateone.js:  Added a 3-second no-matter-what timer for meta key emulation that ensures GateOne.Input.metaHeld gets set to `false` after three seconds if a keyup event never gets fired (works around a problem on Macs when users ⌘-tab).