Added emerge @preserved-rebuild

* Added emerge @preserved-rebuild:
  * to gentmaint-consistent, gentmaint-update
Updated help descriptions
Changed sourceforce.net to sf.net in scripts
Added gentmaint-version and use it

* Added gentmaint-version and use it:
  * script is automatically generated by release packager
  * prints package banner and release info
  * use in all scripts that use StdOut