[BioC] limma 1.5.1 ok under R 1.8 or R 1.9

[Gordon Smyth]

 From today (limma version 1.5.1) the development version of limma can be 
run under either R 1.8.1 or R 1.9.0dev. So there is again only one 
up-to-date version of the package and it can be obtained from the BioC 
development site.

Gordon