adminpack: Revoke EXECUTE on pg_logfile_rotate()

In 9.6, we moved a number of functions over to using the GRANT system to
control access instead of having hard-coded superuser checks.

As it turns out, adminpack was creating another function in the catalog
for one of those backend functions where the superuser check was
removed, specifically pg_rotate_logfile(), but it didn't get the memo
about having to REVOKE EXECUTE on the alternative-name function
(pg_logfile_rotate()), meaning that in any installations with adminpack
on 9.6 and higher, any user is able to run the pg_logfile_rotate()
function, which then calls pg_rotate_logfile() and rotates the logfile.

Fix by adding a new version of adminpack (1.1) which handles the REVOKE.
As this function should have only been available to the superuser, this
is a security issue, albeit a minor one.

In HEAD, move the changes implemented for adminpack up to be adminpack
2.0 instead of 1.1.

Security: CVE-2018-1115
