[RFC] obtaining the function call stack

Hi,

This is a preliminary request for comments on obtaining a function call
stack.  I've been trying to dodge the issue by exporting elog.c internal
state (errcontext), but that turns out to be unfeasible and it's such a
horrid kludge anyway.

So, the idea is to have a stack maintained by the function manager; each
called function enters an element in it containing the interesting
information about the function.  We'd have another function that would
return this stack as a result set.  (With this arrangement, the topmost
element would always appear to be this "peek" function.)

I haven't looked at the code to see how this would actually be
implemented, so I don't have more details to offer.  Does anybody have
opinions on the matter?

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support