Allow installation to proceed when CLT is dispersed

@benhoskings commit message should say it all. mind cutting a release with this?
Ahh, I see. It is attempting to meet the dep but the 'xcode tools' dep doesn't really have a meet block, because the install can't be automated; it just prints the "install via the App Store" message.

The interaction of the check and the dep leads to a crappy result, I agree. Let me have a think about the best approach.