packaging: Fixed problem that bin/umount.xtreemfs was deleted by "make clean"...

packaging: Fixed problem that bin/umount.xtreemfs was deleted by "make clean" when builind the source tarball.

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@3655 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534