[FIXED JENKINS-15120]

- integrated the newer release of remoting
- jar caching won't work with class file directory, so plugin
  WEB-INF/classes are now exploded as WEB-INF/lib/classes.jar
  (This should also solve the problem of slow plugin extraction in the
  presene of Anti-virus software on Windows.)
- because the structure of the exploded jar file has changed, I changed
  the up-to-date check timestamp file name to force re-extraction in
  existing installations.