[BioC] Fixes to limma treat() function

[Gordon K Smyth]

I've committed a major bug fix to the treat() function of the limma 
package.  Users of this function should re-install limma 2.18.2 or 2.19.2 
from Bioconductor.

I've introduced a new function topTreat().  Here's an example calling 
sequence:

   fit <- lmFit(y, design)
   fit <- treat(fit, lfc=0.1)
   topTreat(fit, coef=2)

Best wishes
Gordon