typo: reoppsitory -> repository
check if tag name is already in use (fail gracefully and not with assertion)
FIX: allow for spaces in tag descriptions
allow for moving of tags
allow for spaces in tag descriptions
cleanup sanity checks for tag manipulations
Merge pull request #181 from reneme/fix_history_controls

FIX: history controls in cvmfs_server

This provides some improvements of the history handling in cvmfs_server.
In particular:
    possibility to use tag descriptions with spaces
    sanity check for duplicating tag names