Bs tooltip string value

Under some circumstances the `$observe` handlers are firing after the `$watch` handlers. When the tooltip is nested in an `ngRepeat` is one of these cases. When this would occur the `$observe` handler for the `title` attr was clobbering the `scope.title` set by the `bsTooltip` watcher. Even when no value was specified for the `title` attribute. This would result in the title specified via the `bsTooltip` attr being overwritten with `undefined`. This manifested itself with the tooltip not displaying as expected.

Here is an example:
http://plnkr.co/rtojtWs9fEBgDJawXakT?p=preview