In actor.usr_merge(): For each *_bucket table, transfer the buckets

In actor.usr_merge(): For each *_bucket table, transfer the buckets
belonging to the source user into the custody of the destination user.

In order to avoid colliding with an existing bucket owned by the
destination user, append the source user's id (in parenthesese) to the
name.  If you still get a collision, add successive spaces to the name
and keep trying until you succeed.

git-svn-id: svn://svn.open-ils.org/ILS/trunk@13481 dcc99617-32d9-48b4-a31d-7c20da2025e4