Fix format security errors with hardening build flags

These problems were found while building with the hardening options used
by Debian. In order to prevent introducing new unsafe constructs, the
options -Wformat" and -Werror=format-security are addeded to the CFLAGS
by configure.ac if the compiler supports them.

Also, a small spelling fix in posix-aio.c is included.

Change-Id: I1034311644fa3c21bc5a7b842c41a3ca79108b3f
BUG: 887278
Original-author: Patrick Matthäi <pmatthaei@debian.org>
Signed-off-by: Niels de Vos <ndevos@redhat.com>
Reviewed-on: http://review.gluster.org/4311
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Kaleb KEITHLEY <kkeithle@redhat.com>
Reviewed-by: Anand Avati <avati@redhat.com>