Allow using data-enhance="true" to override a previous false.

While importing some legacy pages into the jqm framework I had to switch off the auto-enhancing on some set of pages. Later when I started to migrate some of them I wanted to turn on the enhancing on them, but only on them, by using data-enhance="true" on a child of the included html, but jqm didn't support this.
This patch adds the support for this feature.