Fix remote spec load when using multiple servers and a lock file

Scenario:

Gemfile:
source 'http://server1'
source 'http://server2'
gem 'A'

Gemfile.lock: (Produced by bundler 1.0.21)
gem 'A', '1.0'
gem 'B', '1.2'

Server 1:
- Has gem A which requires gem B >= 1.0
- Has gem B 1.0 available

Server 2:
- Has gem B 1.2 available

Bundler will report gem B 1.2 cannot be found.

This patch fixes this issue, however, I have no idea how/where to put tests for this case.