Revision 1540479

FELIX-4310, FELIX-4282 - mixed Jetty versions:

- the cometd project referenced an older version of Jetty (7.6.3),
  which is not directly incorrect, but not inline with the other
  projects;
- due to this, classes of two different Jetty versions were inlined
  in the http.bundle project, causing subtle errors at runtime;
- upgraded Cometd to 2.7.0 as Cometd 2.4.2 uses Jetty 7.6.3 as
  compile-time dependency, while the 2.7.0 uses Jetty 7.6.13;
- reverted changes for Jetty 9 to make use of latest Jetty 7.6.13
  version (for fix-release);
- updated POMs to use version-properties for most of the used
  libraries. Also downgraded the version numbers in preparation for
  a fix-release.