Auto merge of #1577 - alexcrichton:issue-1567, r=brson

Previously if a package had been activated without the default feature and then
it was attempted to be reactivated with the default feature, resolution wouldn't
continue and actually activate the default feature. This means that the
fingerprint on the other end of compilation would be slightly different because
the set of activated features would be slightly different, causing spurious
recompiles.

Closes #1567