Add more exceptions on pluralization for -fe/-ve endings

I'm not sure what's the best way to deal with these pluralization exceptions - if adding in the Rails core or only in the applications, but currently without this commit `'olive'.pluralize => 'olifes'` instead of 'olives'.

I tried to update the plural/singular regular expressions that match 'olive', but I got some conflicts with 'knife', 'wife', 'life' etc.

* wi*fe* => wi*ves*
* sa*fe* => sa*fes*

--

* wi*ves* => wi*fe*
* oli*ves* => oli*ve*