configury: set SPECL correctly in VPATH builds.

* specs/specs.mk (SPECL_ENV): Make sure SPECL is set correctly
for VPATH builds, per `make distcheck`.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
maint: post-release administrivia.

* configure.ac (AC_INIT): Bump release version to 12.
* NEWS: Add header line for next release.
* .prev-version: Record previous version.
* ./local.mk (old_NEWS_hash): Auto-update.

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