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.