* passing context in layer calls
* more contexting
* clair folder and context in handlers
* fixed token transport to reuse request context
* tests
* taking out context pass in server handlers
* Test for TokenTransport proving memory leak
* Fix memory leak on wrong auth challenge header
* Add test for memory leak during authentication
The body of the first request must be closed before doing the request to
the authentication service
* Fix memory leak during authentication
Rather than returning an error that requires pattern-matching from
`parseChallenge` when the challenge header requires basic
authentication, return a distinguished error value. This makes checking
for this error a bit easier.
This commit also updates the check in `r.Headers` to use the new error
value and adds a couple of regression tests.
