Remove unneeded loadClass calls
Rewrite RuntimTest.testWrite to not depend on the ByteArrayWriter class
Replace existing zip implementation with jszip v2.4.0

jszip has a much cleaner API than the existing RawDeflate version. In
addition, jszip supports creation of a compressed output stream.

As it's non-trivial to make jszip behave with closure compiler, a second
concat-only step has been during compilation to include any 3rd party
dependencies.