Support for -platformsdk option for ADT package command

[sfreeland]

Typically the latest AIR SDK ships with a bundled iOS SDK that's a few versions behind. When the latest iOS SDK is required, the -platformsdk option must be passed to ADT, specifying the location of an iOS SDK installation external to the AIR SDK.

I'm not sure whether the best way to handle this in pom.xml would be as a simple configuration flag or a dependency.

[sfreeland]

Working on implementing this today.