r14631: Add {,un}installpammodules rule and add it to the install rule.

r14631: Add {,un}installpammodules rule and add it to the install rule.

Nothing happens if PAM_MODULES is empty which is our default.

The default destination dir is "${LIBDIR}/security".  It's possible to
overwrite the default with --with-pammodulesdir while calling configure.
(This used to be commit 7163c6860549378fa63907048c4eb34fe81835cc)