Fixed build warnings in stack

Fixed build warnings in stack

OCException's string handling was missing a few items.

ocstack used some creative casting to get a 16 bit value out
of an 8 bit array that could likely result in bad-optimizations
or undefined behavior.

Removed an unused variable.

Change-Id: I9af5d22f450f72d15b793cec57630e8c81f7b5de
Signed-off-by: Erich Keane <erich.keane@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/496
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Sachin Agrawal <sachin.agrawal@intel.com>
Reviewed-by: Sashi Penta <sashi.kumar.penta@intel.com>