Warnings for instance variable not initialized

[thinkerbot]

The context class created in environment.rb raises some warnings due to the @only and @except variables not being initialized. Example:

% echo 'gem "rack"' > Gemfile
% gem bundle
% ruby -w -rvendor/gems/environment -e 'Bundler.require_env(:test)'
./vendor/gems/environment.rb:72: warning: instance variable @only not initialized
./vendor/gems/environment.rb:78: warning: instance variable @except not initialized

The fix is to initialize the variables: bahuvrihi@b388d7248f634dbfddd979dd2ab08132293e0eb1 (note you may just want to cherry pick this commit -- it's off of a branch relating to another issue that hasn't been acted on yet -- http://github.com/wycats/bundler/issues#issue/72).