For #1249

Improved sanitizing of configuration names which have a number prefix.

[Gemfile] Remove libxml2

This has no longer been a dependency of Xcodeproj

Drop support for Ruby 1.8.7

[ResolverSpec] Add a test case for subspec dependencies where not all versions have a subspec with the given name

Fixes #2733.

Molinillo

See https://github.com/CocoaPods/CocoaPods/pull/2637

[Analyzer][LockingDependencyAnalyzer] Use new LockingDependencyAnalyzer to generate_version_locking_dependencies

Tis should now behave more like Bundler

[ResolverSpec] Add uses a Podfile requirement even when a previously declared dependency has a different requirement