MFC lualoader: module-manipulation commands

4634bb1f: lualoader: provide module-manipulation commands

Specifically, we have:

• enable-module
• disable-module
• toggle-module

These can be used to add/remove modules to be loaded or force modules to be
loaded in spite of modules_blacklist. In the typical case, a user is
expected to use them to recover an issue happening due to a module directive
they've added to their loader.conf or because they discover that they've
under-specified what to load.

10aeb6cd: lualoader: config: fix module enabled check

A last minute rewrite left this logically wrong; if it's present in
modules_blacklist, then we do not load it.

7ed84fa1: lualoader: cli: provide a show-module-options loader command

This effectively dumps everything lualoader knows about to the console using
the libsa pager; that particular lua interface was added in r368591.

A pager stub implementation has been added that just dumps the output as-is
as a compat shim for older loader binaries that do not have lpager. This
stub should be moved into a more appropriate .lua file if we add anything
else that needs the pager.

(cherry picked from commit 4634bb1f4052ff5f1c0a423fd8cce11396ca7fd2)
(cherry picked from commit 10aeb6cdab8fb09e2cc3ee2d8b2c68c395481c23)
(cherry picked from commit 7ed84fa14b00cdacfe9b43019cba7a14b33af352)