Make it behave correctly when there are more than two tables being
joined, also.  Update regression test expected outputs.

a config.h #define, and the runtime value can be controlled via SET.

actually a type-coercion problem.  If you have a function defined on
class A, and class B inherits from A, then the function ought to work
on class B as well --- but coerce_type didn't know that.  Now it does.

Implement TIME WITH TIME ZONE type (timetz internal type).
Remap length() for character strings to CHAR_LENGTH() for SQL92
 and to remove the ambiguity with geometric length() functions.
Keep length() for character strings for backward compatibility.
Shrink stored views by removing internal column name list from visible rte.
Implement min(), max() for time and timetz data types.
Implement conversion of TIME to INTERVAL.
Implement abs(), mod(), fac() for the int8 data type.
Rename some math functions to generic names:
 round(), sqrt(), cbrt(), pow(), etc.
Rename NUMERIC power() function to pow().
Fix int2 factorial to calculate result in int4.
Enhance the Oracle compatibility function translate() to work with string
 arguments (from Edwin Ramirez).
Modify pg_proc system table to remove OID holes.

such as bpchar(char_expression, N), and pull out the attrtypmod that
the function is coercing to.  This allows correct deduction of the
column type in examples such as
CREATE VIEW v AS SELECT f1::char(8) FROM tbl;
Formerly we labeled v's column as char-of-unknown-length not char(8).
Also, this change causes the parser not to insert a redundant length
coercion function if the user has explicitly casted an INSERT or UPDATE
expression to the right length.

 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.

  SELECT a FROM t1 tx (a);
Allow join syntax, including queries like
  SELECT * FROM t1 NATURAL JOIN t2;
Update RTE structure to hold column aliases in an Attr structure.