Support huge read-only []byte response bodies

[cipriancraciun]

See issue #469.

[erikdubbelboer]

Can you maybe add some test cases to verify that everything works. And so we can keep it working in the future as well when things change.

[erikdubbelboer]

@cipriancraciun would it be possible for you to add some tests to make sure everything keeps working correctly in the future?

[cipriancraciun]

@cipriancraciun would it be possible for you to add some tests to make sure everything keeps working correctly in the future?

Sorry for deferring this, but I was a little busy. I'll try to add them during these days around new year's eve.

[cipriancraciun]

So I've rebased my two commits based on the latest code, and added a few tests at the end of http_tests.go. Basically I check that the SetBodyRaw actually works as expected, if CopyTo and ResetBody work properly.

If I can make any other changes please let me know.

[erikdubbelboer]

Thanks.