specs: ignore local LUA_INIT and LUA_INIT_5_2 settings.

Fix #53.
* specs/specs.mk (SPECL_ENV): Until the next Specl release is
available, manually reset LUA_INIT and LUA_INIT_5_2.
* bootstrap.conf (buildreq): Add a reminder to clean up after
Specl 12.

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