Add javabean property and user generated setter support to @Bindable AST transformation.

The current version, as of revision 13997, of the @Bindable AST transformation does not support user generated setters or javabeans properties. A javabean property being defined here as a user generated getter and user generated setter with no backing field or at least no groovy property definition.

The attached patch was written against revision 13997 of groovy/beans/BindableASTTransformation.java from SVN. If this is an acceptible solution, I would be glad to generate a patch for the VetoableASTTransformation.