merge-users.pl - Merge two user accounts.
 This script moves activity from one user account to another.
 Specify the two accounts on the command line, e.g.:
 ./merge-users.pl [email protected] [email protected]
 or:
 ./merge-users.pl id:old_userid id:new_userid
 or:
 ./merge-users.pl id:old_userid [email protected]
 Notes: - the new account must already exist.
        - the id:old_userid syntax permits you to migrate
          activity from a deleted account to an existing one.