make exception_start_column.phpt green again, closes #302

Test began to fail with V8 ~5.9.35 which started to report different
column numbers of errors.  Adapt test so it works well with older
and newer versions of V8.

tests/exception_start_column.phpt

@@ -6,15 +6,23 @@ Test V8::executeString() : Test getJsStartColumn on script exception
 <?php
 $v8 = new V8Js();
 
+// V8 started to return different start column numbers,
+// hence let's do two errors and just look at the offset
+
 try {
 	$v8->executeString("print(blar());");
 }
-catch(V8JsScriptException $e) {
-	var_dump($e->getJsStartColumn());
+catch(V8JsScriptException $a) { }
+
+try {
+	$v8->executeString("(null); print(blar());");
 }
+catch(V8JsScriptException $b) { }
+
+var_dump($b->getJsStartColumn() - $a->getJsStartColumn());
 
 ?>
 ===EOF===
 --EXPECT--
-int(6)
+int(8)
 ===EOF===