fix #591 failing template tests due to wrong usage of Syn

After updating Syn in 104a7f2cddcabfe50919ce546518edb119ef24ff, the tests (fixed in this commit)
were failing on IE7 because they were using Syn incorrectly, trying to click on an invisible
element.
fix #589 Considering scrollbars width on Mac

When on mac the method aria.templates.Layout.getScrollbarsWidth() returns zero, due to the fact that on mac the scrollbars are managed differently. So in this case we add 17px in order to consider them and to avoid to crop some content.