Some ruby-build definitions expect the target (parent) directory to exist

[ryanfb]

Some ruby-build definitions expect the target (parent) directory to exist, which sometimes isn't there with a fresh rbenv install, so use mkdir as part of the rbenv-install script.

See: https://gist.github.com/b9adc50e729e94fccb28

[sstephenson]

Do you think we ought to do this in ruby-build instead?

[ryanfb]

Yeah I thought about that, you could instead put it before the cp -R in build_package_copy: https://github.com/sstephenson/ruby-build/blob/master/bin/ruby-build#L171

One issue that might help with is it won't leave behind an empty dir for failed compile installs (though I haven't checked to see if mri/ree/rbx ever have this problem or if it's just JRuby). My logic for putting it in rbenv-install was basically that if you're using ruby-build directly, it's more "obvious" that the parent should exist for the directory you pass it (whereas with rbenv install you're just passing it a version name).

[sstephenson]

Yeah, I think this is an issue with build_package_copy. The prefix doesn't need to exist for autotools installs.

[ryanfb]

Pull request rewritten as suggested.

[sstephenson]

Thanks!