GROOVY-6561 and GROOVY-1642 : Scripts and URLs/URIs

This patch touches quite a few pieces of code and may need further work, but it looks pretty good to me and passes all the tests of course.  These two issues are in one PR because GROOVY-1642 (@ScriptURI) is a good (the only?) way to test GROOVY-6561 (which gets the URL from the command line down the line to where the AST transform can use it).