bundler/bundler — pull request #2948 by dylanahsmith (2014-03-28 18:08:01+00:00)
Title: Use git sha as part of extension directory for git referenced gems.

## Problem

See issue #2947 which this pull request fixes.

## Solution

Monkey patch Gem::Specification#extension_dir so that the source can override the extension directory name if it responds to extension_dir_name, similar to the monkey patch of full_gem_path.