Merge branch 'bc/http-empty-auth'

Some authentication methods do not need username or password, but libcurl needs some hint that it needs to perform authentication. Supplying an empty username and password string is a valid way to do so, but you can set the http.[<url>.]emptyAuth configuration variable to achieve the same, if you find it cleaner. * bc/http-empty-auth: http: add option to try authentication without username