ui-sref-active should be able to match on nested child states.

[noeticpenguin]

Feature Request:

Given a state 'foo' and child state 'foo.bar' ui-sref-active should be able to maintain it's 'active' status on the parent state, while the child state is in view.

plnkr demonstrating usefulness:
http://plnkr.co/edit/UaBV3DPwR6qt3KLTjQ0r?p=preview

Use navigation menu to hit manage flights
Note two flights F-0000, F-0001 neither of which are listed as "active"
Click on one of them.
Border is drawn around selected tab.
Now click on the "search w/ Criteria" button inside the active state.
The "active" state is lost on the selected tab, even though the displayed state is a child of the tab.

Discussed with Caitp in irc.

[caitp]

It's a pretty simple fix, doesn't break any tests and afaik shouldn't be a breaking change. We can talk about the attribute name, I'm not sure what the best one would be, but this can probably make it into the tree in a few days.