- added disk tagging support for Windows Azure (bnc #815809)
  * added function writeVHDTag called in createVHDSubFormatFixed
  * added <type> attribute 'vhdfixedtag' to store the tag following
    the pattern: "[0-9a-f]{8}-([0-9a-f]{4}-){3}[0-9a-f]{12}"
- added .releasetags helper script to find release commits