Implement TIMEZONE_HOUR, TIMEZONE_MINUTE per SQL92 specs.

Check for and properly ignore FOREIGN KEY column constraints
 (already had fixed same for table constraints).
Define USER as synonym for CURRENT_USER per SQL92 specs
 (no longer allowed as bare column name, sorry).
Re-enable HAVING clause but no fixes elsewhere yet.
Make "char" type a synonum for "char(1)" (actually implemented as bpchar).
Compress/compact row-style subselect and operator definitions
 (cut out ~140 lines of code with no change in functionality).
Save string type if specified for DEFAULT clause handling.
Enough for now...