fix(dialog): IE8 fix to not set data() against text nodes.

This is to fix the error message: `Object doesn't support this property or method` when attempting to open a dialog using IE8 and JQuery (with any template that has white-space between, before, or after the top level elements).

I didn't see this fixed in https://github.com/angular-ui/bootstrap/pull/249 . This is the only IE8 issue in `$dialog`, that I am aware of. 

**Edit:** updated description to provide a bit more detail on what problem this is intended to fix.