#588 Fix for CompileTask source maps

This fixes the issue observed in #588.
I believe it does. See [```FileList.iterator()```](https://github.com/apache/ant/blob/master/src/main/org/apache/tools/ant/types/FileList.java#L190); it does the same thing as ```FileList.getFiles()``` (the old method being used) except it wraps the result in an iterator.