erroneous expected output for RESET DateStyle: should be ISO now.
Fix run_check.sh so that test postmaster is started with PGDATESTYLE=ISO,
else the horology test won't pass.
Implement "date/time grand unification".
Transform datetime and timespan into timestamp and interval.
Deprecate datetime and timespan, 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 column identifier 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.
Make NUMERIC a known native type for purposes of type coersion. Not tested.
Previously, dates falling within Unix system time range were run through
a call to localtime() to get the time zone, if it was not specified.
This had the effect that dates with DOMs which were larger than would be
valid for that month were "rotated" into the following months.
