Table versions

Hi all,

I'm trying to create some kind of table version control
system for approximately 300 postgres databases 
ranging in version from 7.1.2 to 7.3.4.

I compared the "pg_dump -s" output between 
the various versions of databases, but the format is inconsistent,
and I can't do diff's to check that table structures are identical
on the various databases this way. 

What I did next, is put a trigger on pg_attribute that should, in theory,
on insert and update, fire up a function that will increment a version
number on a table comment every time a table's structure is modified.
I tried to make the function update a comment on pg_description to
accomplish this. 

I'm having a lot of trouble doing this and testing it, and after plenty tries
it's still not working. I've attached the trigger statement and the plpgsql function.
(There might be a few mistakes, and I haven't attempted to cater for
system columns and  multiple changes yet.)

Can somebody please tell me if what I'm trying will ever work, or
maybe an alternative (easier) way to compare a specific table's 
structure amongst various databases, that are not necessarily 
on the same network, nor of the same version of postgres.  
 
Regards 
Stefan