[xmonad] [patch] Added doShift function in ManageHook

Hi all! While writing an article about xmonad, I've noticed that writing and explaining 'doF . W.shift' in manage hooks code is a bit obscure and cryptic for xmonad novices. So I've added doShift function, which has more user-friendly name and makes possible to avoid 'doF' function, which name might seem strange. -- WBR, Ivan N. Veselov aka sphynx.