dblink.sql not found

I have postgresql91-contrib installed in Centos 6:

# yum list installed postgresql91-contrib
...
Installed Packages
postgresql91-contrib.x86_64 9.1.4-1PGDG.rhel6 @pgdg91

But when I try to use it I get the error:

ERROR:  function dblink(text, text) does not exist
LINE 2: from dblink(
             ^
HINT:  No function matches the given name and argument types. You might need to add explicit type casts.

Also I can't find dblink.sql:

# find / -name dblink.sql

What am I missing?

Regards, Clodoaldo