Ported annotation processing from apt to javac.

This is a manual merge of request #86 by @b23prodtm. The original patch is fantastic, but as expected has a few issues that will be fixed in subsequent commits.
Automatic code reformatting.

Nothing to see here, just a cleanup so that subsequent commits are cleaner.
Made the javac-based Generator compatible with JDK 6.
Restored check that skips generation if the source template has not changed.

Note that javac still always recompiles everything. This makes the build process slower than before (apt was using the already compiled templates as input). Will investigate some other time if this can be mitigated.
Fixed field/method order so that javac output matches apt output.
Finished work on the annotation processing port from apt to javac.

LWJGL now requires JDK 6 or later to build, but will continue to work on Java 5. In this commit: removed native file "last modified time" handling.