auto-creates destination dir of generated stub wrapper

Git doesn't do empty dirs, so the stubwrappers directory
wasn't present, which was preventing these from being generated
properly, thus breaking the build after the migration to github.

Author: Chris Wilper

fcrepo-generate/src/main/java/org/fcrepo/generate/BuildAxisStubWrapper.java

@@ -245,6 +245,7 @@ public static void main(String[] args) {
                 String pkg = args[2];
                 String cls = args[3];
                 File wrapper = new File(args[4]);
+                wrapper.getParentFile().mkdirs();
                 new BuildAxisStubWrapper(stub, template, pkg, cls, wrapper);
             } else {
                 throw new IOException("Must supply " + argCount + " arguments.");