Specify unpenalized groups through group.multiplier

[pbreheny]

One should be able to specify unpenalized groups through group.multiplier, as in:

data(Birthwt)
X <- Birthwt$X
y <- Birthwt$bwt
group <- Birthwt$group
fit <- grpreg(X, y, group, group.multiplier=0:7)

But this doesn't work; they have to be given a group number of 0.