Pause when the window loses focus Pause when the window loses focus

From issue 1534 on googlecode where the patch was first added a year ago!
http://code.google.com/p/corsix-th/issues/detail?id=1534

Adds a config option to pause the game when it loses focus - by default this is off.

Tweaked the original patch from Alan and added a button in the customise menu
added a button for check for updates option at the same time
amended the no heliport message to make it read better
NOTE: That save game version and afterload function will want updating as the actual number will depend on when and if this is merged