Bitwise OR in a group statement

I was wondering if anyone happens to know whether there is an Aggregate function available in Postgres that can do an
ORon a column of the bit varying type. For example I would like to do something as follows: 

bitstring
*--------
1110
0100
1111


SELECT bitwise_or(bitstring) FROM table;

Resulting in:
1111

Any thoughts? Thanks.

- Greg Gazanian
Network Systems Analyst
Technology and Information Services
Arcadia Unified School District