* iswitchb.el (iswitchb-max-to-show): Added a new config variable
which optionally limits the number of names shown in the
minibuffer. Off by default.
(iswitchb-completions): Use `iswitchb-max-to-show'. This speeds
up iswitchb for users with a multitude of open buffers, by showing
only the first and last N/2 buffers in the completion list (which
is enough for C-s/C-r, and to know that more characters need to be
typed to refine the completion list).