Patches for LOCALTIME and regexp, feature list

I've just committed changes to include an SQL99 feature list as an
appendix in the User's Guide. While preparing that I noticed a feature
or two which would be trivial to implement, so we now have LOCALTIME and
LOCALTIMESTAMP function calls per spec (afaict; the spec is very vague
on the behaviors).

I've also removed the ODBC-compatible parentheses on CURRENT_TIMESTAMP
etc and made sure that the ODBC driver handles the case correctly.

More details from the CVS logs are below...

- Thomas

Add LOCALTIME and LOCALTIMESTAMP functions per SQL99 standard.
Remove ODBC-compatible empty parentheses from calls to SQL99 functions
for which these parentheses do not match the standard.
Update the ODBC driver to ensure compatibility with the ODBC standard
for these functions (e.g. CURRENT_TIMESTAMP, CURRENT_USER, etc).
Include a new appendix in the User's Guide which lists the labeled
features
for SQL99 (the labeled features replaced the "basic", "intermediate",
and "advanced" categories from SQL92). features.sgml does not yet split
this list into "supported" and "unsupported" lists.
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...