Allow remove_buffer to delete a buffer without closing the command-t window

[Aster89]

I've just discovered that Ctrl-d deletes the selected buffer. That's great!

However, it would be even greater if the list of matched files didn't close. This way, we could keep writing/rewriting to get other matches and keep deleting buffers as we like. This can come very useful when, after a day of work, one wants to clean the buffer list before saving a session.

I would do the change myself, but that'll take the time I need to learn a bit of ruby.