Update Gerrit commit hook.

etc/gerrit/commit-msg

 #!/bin/sh
-# From Gerrit Code Review 2.4.2
+# From Gerrit Code Review 2.8.1
 #
 # Part of Gerrit Code Review (http://code.google.com/p/gerrit/)
 #
 # limitations under the License.
 #
 
+unset GREP_OPTIONS
+
 CHANGE_ID_AFTER="Bug|Issue"
 MSG="$1"
 
 		return
 	fi
 
+	if test "false" = "`git config --bool --get gerrit.createChangeId`"
+	then
+		return
+	fi
+
 	# Does Change-Id: already exist? if so, exit (no change).
 	if grep -i '^Change-Id:' "$MSG" >/dev/null
 	then
 		if (unprinted) {
 			print "Change-Id: I'"$id"'"
 		}
-	}' "$MSG" > $T && mv $T "$MSG" || rm -f $T
+	}' "$MSG" > "$T" && mv "$T" "$MSG" || rm -f "$T"
 }
 _gen_ChangeIdInput() {
 	echo "tree `git write-tree`"