modules: added support for automatically adding "use namespace X", depending on the -target-player value
* similar to how we add "use namespace AS3"
* symmetric with ASC's -use feature, however we don't have equivalent commandline support yet
QA: Nothing in particular, except for testing the new functionality of -target-player (email me about this)
Doc: Maybe: If we doc about "use namespace AS3" being added to all Flex compiles, we may want to talk about this.
Reviewers: Pete and Erik