Dynamically generating DDL for postgresql object

I'd like to dynamically generate a SQL script that pulls together complete
DDL (CREATE, ALTER, etc.) for specific objects (especially constraints) in
my PostgreSQL 8 database. I want to use this for our development project's
schema migration process, which involves dumping the data, making schema
changes, recreating the database, temporarily removing constraints,
restoring the data, and re-applying the constraints (this last step requires
the dynamic DDL described above).

I've noticed that pgAdmin's "DDL Report" feature can retrieve this DDL for
many types of objects - not sure how much work it has to do to build the SQL
it's displaying here. But I haven't seen anything about getting this
directly from the database using SQL , psql, etc. I've only seen reference
to this as a proposed project on the PostgreSQL
<http://www.postgresql.org/developer/summerofcode.html> Google SoC page

Anyone know how to get object DDL SQL through a script? Ideas on
alternative approaches would also be appreciated.

Thanks,

Mark