packaging: Updated helper script for building the source tarball.

- Updated blacklist of files which should not be put in the source tarball.
- Removing .gitignore files from the source tarball now.
- No longer copying a second directory "xtreemfs-testing" which contains the same information as the "xtreemfs" directory. (The content of this directory is uploaded to the OBS.)

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@3493 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534