How to include Tablefunc as an extension

Hello,

I read through the Postgres doc and many Google results, but it seems still unclear to me how to include additional packages into my postgres database. I see that there are a few installed under "/usr/local/pgsql-9.1/share/extension/" (I am on Lion and installed the Kyngchaos libs). But as I want to install crosstab now, I downloaded the source code for postgres, run a make/install - and now wonder what to do with it. I could eventually load the .sql file as usual; but it seems this should be now avoided, and loaded as an extension. I tried to copy three files (--1.0.sql, --unpackaged.sql and the normal .sql) to the folder and then load it from PgAdmin, but this results in an error message ("could not access file "$libdir/tablefunc"").

Thanks for any hints!