borderRadius getter, specs and consistency

- fix getter bugby behavior for borderRadius
(http://jsfiddle.net/rg4Yp/)
- make result consistent cross-browser
- add specs
simplify, optimize and fix punctuation

Also make this new spec not run if PhantomJS is version 1.x
improvement after review feedback
use indexOf('borderRadius') != -1 instead
Merge pull request #2611 from SergioCrisostomo/fix-2545

borderRadius getter, specs and consistency