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

[hyunsook]

Hi all~!

Currently, the domCache 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.
• 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. :)

[arschmitz]

Thank you for submitting this PR however there has already been a discussion #4052 about this prior and decided this is a feature not a bug and it is on our list of feature requests so im going to close this for now until we decide wether or not to support this.

[hyunsook]

@arschmitz : I'm sorry that I didn't check the #4052 in advance. Thanks for the explanation. :)