Make 4.2/4.3 switchable configuration more robust

Currently, files whose code is changed at build time (for 4.2/4.3 buildability) reside in svn in their respective location. This makes it hard to checkout+patch+build+test+commit, as the build phase modifies the original files, causes changes to go back and forth in svn unnecessarily.

The original files should be kept out of the sight of the javac task, and instead, the manipulated copies should be put in the output folder, providing those to javac instead.