Why I can't install postgresql with rails 4.0.0.rc1 (ruby 2.0)

The page says Bundler has a platform detection and verification problem on Windows 7 x64 with Ruby 2.0, Rails 4.0.0, PostgreSQL 9.2.4 x64, pg 0.15.1, and mysql2 0.3.11. It gives a temporary workaround that edits Gemfile.lock to include the x64 mingw32 version of pg alongside the x86 one.

Reading notes

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• Reports a Bundler platform detection and verification problem on Windows 7 x64 with Ruby 2.0, Rails 4.0.0, PostgreSQL 9.2.4 x64, pg 0.15.1, and mysql2 0.3.11.
• Suggests a manual edit to Gemfile.lock as a temporary workaround.
• Replaces the pg line that lists only pg (0.15.1-x86-mingw32) with one that also includes pg (0.15.1-x64-mingw32).