Search the existing regular expression cache as a ring buffer.

Search the existing regular expression cache as a ring buffer.
Will optimize the case for repeated calls for the same expression,
 which seems to be the most common case. Formerly, always searched
 from the first entry.
May want to look at the least-recently-used algorithm to make sure it
 is identifying the right slots to reclaim. Seems silly to do math when
 it seems that we could simply use an incrementing counter...