CHAMP bags support transients.
Makes a transient-ch-bag whose initial contents are those of b. If
synchronized? is true, all operations on the transient will be serialized via locking;
otherwise, the transient is not thread-safe.
A transient CHAMP bag. Subclass of transient-bag. These print simply as:
#<TRANSIENT-CH-BAG id>
where id is a serial number to identify the instance.
Returns true iff x is an FSet transient CHAMP bag.