Page: Fixed the abnormal operating of _setOptions() for the domCache option.

Hi all~!

Currently, the <code>domCache</code> option of Page widget is not set properly on runtime.
So, to fix this bug, I submit PR.

* origin: You can see the bug of _setOptions() for the domCache option through the following sample page.
http://hyunsook.github.io/jqm-debug/latest/page-domCache.html.
Step 1. Go to that page.
Step 2. Click "set domCache option" button in that page.
Step 3. Test _setOptions() for the domCache option by following the steps to reproduce of the loaded page, [page-caching-switch.html](http://hyunsook.github.io/jqm-debug/latest/page-caching-switch.html).

* modified: You can see that the bug is fixed on the following page.
http://hyunsook.github.io/jqm-debug/latest/page-domCache_after.html

If there are any problems or mistakes on that PR, please let me know. 
Thanks in advance. :)