maint: bump revision to 31.

* configure.ac (AC_INIT): Bump release revision to 31.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
posix: fix a typo in tc[gs]etattr constant definitions.

* ext/posix/posix.c (VTOP): Changed spelling from this...
(VSTOP): ...to this.

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