Actually it is kinda complicated:
dev(9.1.9, for which pgadmin3 complains w/ that error)postgres=# \dx+ adminpack
Objects in extension "adminpack"
Object Description
-------------------------------------------
function pg_file_length(text)
function pg_file_read(text,bigint,bigint)
function pg_file_rename(text,text)
function pg_file_rename(text,text,text)
function pg_file_unlink(text)
function pg_file_write(text,text,boolean)
function pg_logdir_ls()
function pg_logfile_rotate()
(8 rows)
Did not find any extension named "adminpack".