handle 'upgrade' in comma-separated connection header

[minrk]

Firefox sends keep-alive, upgrade, not just upgrade, which was being turned into close.

[minrk]

closes #690

[indexzero]

This is better fixed with a regular expression.

[minrk]

Thanks, uses a regular expression now.

[jcrugzz]

@minrk only problem I have here is that we will probably leak a socket with keep-alive true and having agent = false but firefox will be the only case.

In regards to the regex, I think you might want .test to get a proper truthy value and to call it on the regex itself. Could you also add a test for this? Appreciate the contribution! :)

[minrk]

Uses .test now, and includes a couple of tests.

[jcrugzz]

@minrk excellent, thank you!

[indexzero]

Worth noting that the regular expression instance need not be constructed every time. It's a small perf optimization so I'm not sure how meaningful it would be.