configury: be more sympathetic to library module packagers.

* Makefile.am (LUA_CPATH): Set to ';' unless overriddeb by the
environment.
(EXTRA_LTLIBRARIES, lib_LTLIBRARIES): New declarations.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
sanity: support local configuration.

* bulid-aux/sanity.mk: Include build-aux/sanity.cfg if available.
(sc_prohibit_strcmp): Don't flag `strncpy()` as an invocation.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>