Tweaking of modselection tab

Fix coordinates of borders, redraw borders after erasing by pop-up window, moving a hint in proper place. Done instead of #5918.
It should looks like this:
![world](https://f.cloud.github.com/assets/5421954/2073549/5d193b44-8d60-11e3-8619-f685515fa57c.png)
Note: multiple copies of mods are done for illustration purpose only.