Ignore rubinius-only gems when running bundle install --local on MRI

[mvz]

This is a fix for #2774. Probably, there are other cases like it which require a more thorough fix. For example, I'm guessing Bundler will try to find MRI 1.8-only gems when installing under MRI 2.0. I'll comment more on this later.

[mvz]

A more thorough fix could go like this:

• Store platforms like :mri, :jruby, :mingw_18 in Gemfile.lock, instead of the current ruby, java. This way, these platforms use the same codes as the platform specifications in Gemfile.
• Fill @dependencies in lib/bundler/definition.rb by asking current_ruby.mri_18? etc., instead of using Bundler.rubygems.platforms. This will create more specific platforms to match with the dependency's platforms, and allow a direct match instead of going through PLATFORM_MAP.

As this is a bit more involved, and likely to be incompatible with Bundler 1.x's behavior, I'd like a bit of feedback on this plan before I start coding.

[indirect]

This makes rubinius a platform, and so it needs :rbx_18 and :rbx_19 etc if it's going to be able to distinguish those things. A fix for that being a bad way to declare platforms is an open ticket, #2691.

The "platforms" in the lockfile are actually rubygems platforms, which are a subset of Bundler platforms, so I think fixing platform locking in Bundler will take a few things coming together at once:

Once we've implemented #2691 (which will break backwards compatibility by itself), and started to respect each gem's required ruby version without platform blocks (which is part of the new index work that will be in the next minor release), then we can (I think) start to just check the platform we are on against the platform the gem says it works on. Ultimately, I would like platform blocks to be completely unnecessary, although there may need to be separate Gemfile sections for each Rubygems platform.

[indirect]

Merging this pull request has created new warning output when running the tests:

WARNING:  Skipping misnamed gem: ./gems/only_rbx-1.0-unknown.gem should be named only_rbx-1.0-unknown (only_rbx-1.0-rbx)

Do you think you could clean that up?

[mvz]

@indirect I'll take a look at it.