Adding ability to filter specs before running

[Keir Lawson]

Hi,

I submitted this ticket here: https://github.com/jasmine/jasmine/issues/865 - if its the sort of feature that would likely have a PR accepted I wouldn't mind working on this? I was thinking a callback to cancel a given test could be passed to specStarted to allow it to be cancelled just before it would be run.  What do folk think?

Thanks

Keir