Fixed WarmUpSetsForCombinationPolicy to take into account sets that have mixed mime types.
For instance, when including the diagnostics package, the FubuMVC.TwitterBootstrap has a set named twitterbootstrap that mixes css and js assets.
Updated WarmUpSetsForCombinationPolicyTester.
Merge pull request #10 from emiaj/warm-up-policy-mixed-mime-types

Fixed WarmUpSetsForCombinationPolicy to take into account sets that have...