Add failing tests when using es5-shim and transChoice in MSIE8
Prevent iterating over shim-ed Array.prototype methods.

Iterating over _parts in transChoice using the 'in' operator pushed the 
shim-ed methods into the _standardRules array. One of that methods
itself would then be returned as plural position 0 in Microsoft 
Internet Explorer 8.
Merge pull request #100 from bvleur/es5-shim-msie8-transchoice-fix

Using transChoice with es5-shim in MSIE8 fails