Fix cursor colour

Fixes #502. It is not necessary to refresh the cursor when changing the evil
state in a buffer that is not displayed in some window, because as soon as the
buffer is displayed somewhere, `evil-refresh-cursor` is called as part of the
`window-configuration-change-hook` or as advice to `select-window`.

evil-core.el

@@ -1279,7 +1279,8 @@ If ARG is nil, don't display a message in the echo area.%s" name doc)
                  (when deactivate-current-input-method-function
                    (deactivate-input-method)))
                (unless evil-no-display
-                 (evil-refresh-cursor ',state)
+                 (when (get-buffer-window (current-buffer) t)
+                   (evil-refresh-cursor ',state))
                  (evil-refresh-mode-line ',state))
                ,@body
                (run-hooks ',entry-hook)