[xmonad] Merged functionality from X.L.ThreeColumnsMiddle into X.L.ThreeColumns (and some new features)

[Adam Vogt]

I've pushed these:

Sat Apr 25 12:17:10 EDT 2009  Adam Vogt <vogt.adam at gmail.com>
  * Export ThreeColMid from L.ThreeColumnsMiddle

  The configs that import it should continue to work with this module, though the
  type of the ThreeColMid constructor is now ThreeCol (previously ThreeColMid).

I doubt that many configs use ThreeColMid, since it is darcs-only. The 
compatibility module added by this patch might be worth removing before the 
next release?

Tue Apr 14 02:18:19 EDT 2009  Adam Vogt <vogt.adam at gmail.com>
  * ThreeColumns support middle column, with more backwards compatiblity

Sat Apr 11 07:36:36 EDT 2009  Anders Engstrom <ankaan at gmail.com>
  * X.L.ThreeColumnsMiddle merged into X.L.ThreeColumns with some new features

Thanks