BUG #2311: Toast table chunk_id overflow

The following bug has been logged online:

Bug reference:      2311
Logged by:          Chris Hodgson
Email address:      chodgson@refractions.net
PostgreSQL version: 7.4.7
Operating system:   Linux Fedora Core 3
Description:        Toast table chunk_id overflow
Details:

If you cycle through enough id's in your toast tables, the chunk_id goes
past 2^32 and wraps around, leaving you  in an intermittent error state.
Inserting further toasted chunks will fail depending on whether that
particular next id from the sequence is already in the table or not.

It really shouldn't be possible to get into this state. There is obviously a
hard limitation of using 4-byte integers as ids for the toasted chunks... I
don't know what the solution is, but at very least an error message that is
more clear about what has happened than repeated, seemingly random
occurences of "duplicate key in table pg_toast.pg_toast_1834831156_index".