fix(tab): IE9 disabled attr renders grey text on enabled tab

[leonardseymore]

This issue can be seen on the boostrap UI page using IE9. The second tab looks disabled when it is really enabled:
http://angular-ui.github.io/bootstrap/#/tabs

• IE9 renders elements with 'disabled' property with grey text
• Tabs are rendered with grey text even if they are not disabled
• By renaming attribute to 'disable' instead of 'disabled' tabs with dynamic 'disable' attribute still render correctly

[tallsam]

This also fixes an accessibility issue in IE9 where you can't select a tab using the keyboard because disabled elements are excluded from tabIndex. +1

On the other hand it will break existing implementations.. :(

[leonardseymore]

What about supporting both attributes and marking "disabled" in the APIs as deprecated?

[wesleycho]

This would require a documentation update.

I think this would be a good breaking change, as using the disabled attribute by the directive currently is bad.

Can you add the documentation change required?

[chrisirhc]

@leonardseymore I like the idea of supporting both attributes (disable, disabled) and dropping the disabled attribute later on. I think this directive is probably used in many places.

We'll need to update the README of the tabs directive to include this information of deprecation.

[wesleycho]

We are deprecating support for disabled then in the meantime? That sounds sensible to me in this case.

[chrisirhc]

Yep that's right, we should deprecate the use of disabled. We can log a warning whenever disabled is used unless it's suppressed, similar to #3497 .

[leonardseymore]

I have made some more changes based on the comments.

[chrisirhc]

How about:

Note that this was previously the `disabled` attribute.

[wesleycho]

Or

Note that this was previously the `disabled` attribute, which is now deprecated.

[chrisirhc]

Looks mostly good to me. Maybe just documentation wording can be improved.

[wesleycho]

We can probably merge this in and patch the documentation change we want - no need to hold this up longer I think.

[wesleycho]

Thanks for this find and fix - it should go out when we release 0.13.0.