roundoff problem in time datatype

Inserting into a time field with limited precision rounds off, which
is good except for this case:

regression=# select '23:59:59.9'::time(0);
time
----------
24:00:00
(1 row)

This is bad because:

regression=# select '24:00:00'::time(0);
ERROR: date/time field value out of range: "24:00:00"

which means that data originally accepted will fail to dump and reload.

I see this behavior in all versions back to 7.3. 7.2 was even more
broken:

regression=# select '23:59:59.9'::time(0);
time
----------
00:00:00
(1 row)

I think the correct behavior has to be to check for overflow again
after rounding off. Alternatively: why are we forbidding the value
24:00:00 anyway? Is there a reason not to allow the hours field
to exceed 23?

regards, tom lane