Allow group/bundle logic to be overridden to force concatenation

[westonruter]

We can add a filter here so that the user can force dependencies to be concatenated even though they have different dependency attributes and would thus normally be concatenated in separate bundles.

See suggestion from @lkraav:

If testing should show no issues, I would like to combine JS and CSS into single groups.

From browsing through, I don't think 0.9.2 has this code, but am I missing something?

[lkraav]

Thanks. I'm too overloaded for at least a week to try to patch this, hopefully someone else can prototype something sooner.

[nash-ye]

hmm, Can you describe it more?! Reasons? Benefits?