select: issue #245 fix, pull request #267 bugfix

1. Fixing https://github.com/mgcrea/angular-strap/issues/245 without tampering with other vendors code.
2. https://github.com/mgcrea/angular-strap/pull/267 bugfix -- changes should be watched as in ng-options directive in angular core (using $parse instead of simple key lookup which fails when one has a dot in the model)
3. Code clean up