Vendor gem failing rake gems:build

I've got a problem with building vendored gems. If the gem is not also system-installed, it fails to build the gem. The error displayed is:

mathie@Tullibardine golflinks (master) $ rake gems:build --trace
(in /Users/mathie/Development/Rubaidh/ruby/rails_apps/golflinks)
** Invoke gems:build (first_time)
** Execute gems:build
rake aborted!
undefined method `full_name' for nil:NilClass
/Users/mathie/Development/Rubaidh/ruby/rails_apps/golflinks/config/../vendor/rails/railties/lib/rails/gem_dependency.rb:287:in `unpacked_gem_directory'
/Users/mathie/Development/Rubaidh/ruby/rails_apps/golflinks/config/../vendor/rails/railties/lib/rails/gem_dependency.rb:291:in `unpacked_specification_filename'
/Users/mathie/Development/Rubaidh/ruby/rails_apps/golflinks/config/../vendor/rails/railties/lib/rails/gem_dependency.rb:174:in `build'
/Users/mathie/Development/Rubaidh/ruby/rails_apps/golflinks/vendor/rails/activesupport/lib/active_support/core_ext/symbol.rb:11:in `__send__'
/Users/mathie/Development/Rubaidh/ruby/rails_apps/golflinks/vendor/rails/activesupport/lib/active_support/core_ext/symbol.rb:11:in `to_proc'
/Users/mathie/Development/Rubaidh/ruby/rails_apps/golflinks/vendor/rails/railties/lib/tasks/gems.rake:23:in `each'
/Users/mathie/Development/Rubaidh/ruby/rails_apps/golflinks/vendor/rails/railties/lib/tasks/gems.rake:23
/Library/Ruby/Gems/1.8/gems/rake-0.8.7/lib/rake.rb:636:in `call'
/Library/Ruby/Gems/1.8/gems/rake-0.8.7/lib/rake.rb:636:in `execute'
/Library/Ruby/Gems/1.8/gems/rake-0.8.7/lib/rake.rb:631:in `each'
/Library/Ruby/Gems/1.8/gems/rake-0.8.7/lib/rake.rb:631:in `execute'
/Library/Ruby/Gems/1.8/gems/rake-0.8.7/lib/rake.rb:597:in `invoke_with_call_chain'
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/monitor.rb:242:in `synchronize'
/Library/Ruby/Gems/1.8/gems/rake-0.8.7/lib/rake.rb:590:in `invoke_with_call_chain'
/Library/Ruby/Gems/1.8/gems/rake-0.8.7/lib/rake.rb:583:in `invoke'
/Library/Ruby/Gems/1.8/gems/rake-0.8.7/lib/rake.rb:2051:in `invoke_task'
/Library/Ruby/Gems/1.8/gems/rake-0.8.7/lib/rake.rb:2029:in `top_level'
/Library/Ruby/Gems/1.8/gems/rake-0.8.7/lib/rake.rb:2029:in `each'
/Library/Ruby/Gems/1.8/gems/rake-0.8.7/lib/rake.rb:2029:in `top_level'
/Library/Ruby/Gems/1.8/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling'
/Library/Ruby/Gems/1.8/gems/rake-0.8.7/lib/rake.rb:2023:in `top_level'
/Library/Ruby/Gems/1.8/gems/rake-0.8.7/lib/rake.rb:2001:in `run'
/Library/Ruby/Gems/1.8/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling'
/Library/Ruby/Gems/1.8/gems/rake-0.8.7/lib/rake.rb:1998:in `run'
/Library/Ruby/Gems/1.8/gems/rake-0.8.7/bin/rake:31
/usr/bin/rake:19:in `load'
/usr/bin/rake:19

The solution seems to be to make sure that the gem's specification can successfully be loaded by always adding the load path before attempting to build the gem. This seems somewhat convoluted, but is the only approach I tried that actually works. So, attached is a patch that makes it work.