_negative numeric option

Hi Jan,

I added a new suffix into singular/plural options: _negative. This option is supposed to be selected when count is 0.

In my opinion that makes sense because let's say we have a phrase: I was here __count__ years ago. When count is 0 it should be for example: I've never been here before. Tests included and seems they pass

A a small note about the pull request. I cloned from your git repository, but for some reason 1.6.1pre was cloned and during push I had to merge all other (152) changes. I hope nothing is broken - git scares me from periodically.

If you consider the change useful - you may just grab changes from the pre-last revision and ignore all of the merge stuff.

Thanks,
Dmitry