Versioning Schema/Stored Procedures

hi all,

We installed a first version (1.0.0.1) of our schema. then came a few
patches we had for a few stored procedures and tables (1.0.0.2). Then even
more (1.0.0.3) (1.0.0.4). Some chose to upgrade to version 1.0.0.3 and stick
to it, while some others chose to upgrade to 1.0.0.4.

Now when i have some more schema updates, how should i find out what
(incremental) updates the client needs?

One way might be to store [ 'version', 'schema', 'Date_time_change',
'User_who_Changed' ] in a table. But i want to store the versions for each
table/stored procedures/views. I could create a table to store these
components with similar details. But i do not want to duplicate the work. I
just want to upgrade the components i need to, so as to avoid downtime for
teh applications taht do not need the component.

Is it possible to modify pg_class to have another 'version' column so that i
can version each relation and other components?
Is there a better way to do schema versioing to the level of tables, stored
procedures and views?

thanks,
vish