GUC temp_tablespaces (updated)

Hi,

This is an updated patch based on conversation on -hackers, basically
it adds a hint to the error thrown by DROP TABLESPACE when it's not
empty and there are temp files older than postmaster startup.

i had to remove PgRemoveTempFiles() to test the patch (what i dificult
task is to crash the server ;)

btw, I tried to send it to the same conversation but it never arrives
so i'm sending it to -patches.

-- 
regards,
Jaime Casanova

"Programming today is a race between software engineers striving to
build bigger and better idiot-proof programs and the universe trying
to produce bigger and better idiots.
So far, the universe is winning."
                                       Richard Cook