BUG #7661: pgstattuple from unpackaged fails on old installation

The following bug has been logged on the website:

Bug reference:      7661
Logged by:          Stuart Bishop
Email address:      stuart@stuartbishop.net
PostgreSQL version: 9.1.6
Operating system:   Ubuntu 12.04
Description:        =


The pgstattuple upgrade from unpackaged script expects the pgstatindex
function to exist, but it does not on particularly old databases (My
pgstattuple originally installed with 8.3 or 8.4?).

# create extension pgstattuple;
ERROR:  function "pgstattuple" already exists with same argument types
# create extension if not exists pgstattuple from unpackaged;
ERROR:  function pgstatindex(text) does not exist