Date/time types: big change

I've just committed changes to "reunify" the date/time types.
"timestamp" and "interval" are now the two primary date/time types for
users. Also, I've changed the default date style to "ISO" (not just in
time for Y2K, but we'll be ready for "Y3K").

Also, I made some changes to have NUMERIC be a "known" type for
purposes of implicit type coersion, but have not tested to see if the
underlying conversion functions are available.

initdb required (and enforced by a catalog version change).

Regression tests pass, except for the rules test due to ongoing rules
formatting work.
                 - Thomas

The detailed change log:

Make NUMERIC a known native type for purposes of type coersion. Not
tested.
Make ISO date style (e.g. "2000-02-16 09:33") the default.
Implement "date/time grand unification".Transform datetime and timespan into timestamp and interval.Deprecate datetime
andtimespan, though translate to new types in
 
gram.y.Transform all datetime and timespan catalog entries into new types.Make "INTERVAL" reserved word allowed as a
columnidentifier in
 
gram.y.Remove dt.h, dt.c files, and retarget datetime.h, datetime.c as
utility routines for all date/time types.date.{h,c} now deals with date, time types.timestamp.{h,c} now deals with
timestamp,interval types.nabstime.{h,c} now deals with abstime, reltime, tinterval types.
 
All regression tests pass except for rules.sql (unrelated).

-- 
Thomas Lockhart                lockhart@alumni.caltech.edu
South Pasadena, California