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