[BioC] genelist reading for GenePix data

[Gordon Smyth]

I'm going to change read.maimages() in the limma package so that for 
GenePix data the genelist is read from the annotation information in the 
gpr files rather than from the gal file as at present. This will mean than 
limma will no longer need the gal file at all. If anyone can think of a 
reason why this isn't a good idea, let me know.

Cheers
Gordon