* drain buffer correctly in httpupgrade
it seems the recently added httupgrade testsuite is causing timeouts on master
i have no evidence this is the real issue, but it feels to me that the
server could accidentally over-read, and then the encapsulated
connection will block forever trying to read data
let's test it in CI a couple of times, i don't have a way to reproduce
the issue
* correctly drain buffer, again
* preserve exact header casing when using httpupgrade
* fix capitalization of websocket
* oops, we dont need net/url either
* restore old codepath when there are no headers
