Debugging printf.

The buildbot printed "expr: syntax error", presumably from this, but
that oh-so-descriptive error message doesn't indicate what the problem
is, and just about any string should be valid as the left-hand operand
of the : operator.

Change-Id: I1140522357b8df07e4183bf0eb8c5fa9fbe275e4
Reviewed-on: https://code.wireshark.org/review/8827
Reviewed-by: Guy Harris <guy@alum.mit.edu>

test/run_and_catch_crashes

@@ -39,6 +39,7 @@ then
 		do
 			shift
 		done
+echo last expr command was expr "$1" : ".*=.*"
 	fi
 	if [ -x "$1" ]
 	then