Setting version to an empty string in tests

Check for nil and length on version in package/rubygems tests

In gemspec test change @new_resource.instance_variable_set()
to @new_resource.version()
Fix installer_version_string to be an array on prerelease parameter.
Merge branch 'empty_version' of github.com:lucywyman/chef
Contribution information for https://github.com/opscode/chef/pull/2452.
Merge branch 'fix_prerelease_parameter' of github.com:Daegalus/chef
Contribution information for https://github.com/opscode/chef/pull/2439.
Merge pull request #2483 from opscode/sersut/contrib-pass

Merge pass for contributions.