Support for "Open tab next to current", and "fix" C-c behaviour

This isn't a "real" pull request, in the sense that I know these are almost certainly unsuitable for merging in their current state.

However, these are real problems that I faced with Vimperator for ages, and finally got around to fixing.

I'm very interested in working to fix these up so that they are customisable (and so don't break behaviour for other users), and so ARE suitable for merging into the main code (so that others in the same position as me can benefit from them, and so that I don't get caught out losing these changes again with future Vimperator updates).  Feedback very very welcome.