CHEF-4890: Allow gem upgrades

This was preventing chef from finding the candidate version when
upgrading a gem and assuming there was nothing to do
CHANGELOG update for https://github.com/opscode/chef/pull/2197.
CHANGELOG update for https://github.com/opscode/chef/pull/2193.
Spec and CHANGELOG info for: https://github.com/opscode/chef/pull/1184
Merge branch 'CHEF-4890' of github.com:rathers/chef into sersut/doc-updates
Merge pull request #2201 from opscode/sersut/doc-updates

CHANGELOG update and spec for gem_package upgrade fix