crashinfo: Get local variable values in the gdb backtrace

This should make crash reports a bit more useful without having to ask
for additional information.

Reviewed by:	imp
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D42465

(cherry picked from commit 3e356fb885)

usr.sbin/crashinfo/crashinfo.sh

@@ -236,7 +236,7 @@ echo
 # kgdb via stdin and have to use a temporary file instead.
 file=`mktemp /tmp/crashinfo.XXXXXX`
 if [ $? -eq 0 ]; then
-	echo "bt" >> $file
+	echo "bt -full" >> $file
 	echo "quit" >> $file
 	${GDB%gdb}kgdb $KERNEL $VMCORE < $file
 	rm -f $file