update javac handling of module names

javac should give a warning when a module name is declared if any of the component identifiers end in a digit.

* warn for digits at the end of each identifier in a qualified module
name, when the module is *declared*.

     WARN: module m1 { }
     WARN: module m1.any { }
     NO WARN: module m { requires m1; requires m1.any; }