Tooltip issues

[pkozlowski-opensource]

Based on discussion in #72 looks like there are still issues with the tooltip:

Oops, sorry for sending you a bad version! Here's the version I meant to send:
http://plnkr.co/edit/1GiwHv
That version demonstrates there's still a problem when you give a tooltip to a link whose href is bound to a value that is initially falsey: even after the value changes to something truthy, the href attribute stays set to nothing.

[joshdmiller]

It looks like all the attributes are being evaluated within the isolate scope. I'll look into this.

[pkozlowski-opensource]

Report on SO, just in case, so we don't introduce regressions while fixing this bug:
http://stackoverflow.com/questions/14454283/ui-bootstrap-tooltip-doesnt-work-when-used-with-ng-repeat

[joshdmiller]

@pkozlowski-opensource I included a test in the last PR to cover that specific case (ngRepeat), so we should be okay.

I may not have a chance to look into this until Wednesday/Thursday.

[lanterndev]

see #132