* This fixes https://github.com/bitly/oauth2_proxy/issues/205
* Add new boolean option -pass-user-headers
to control whether X-Forwarded-User and X-Forwarded-Email
headers will be set (as opposed to HTTP BASIC auth)
* This is required e.g. for grafana [1] where
X-Forwarded-User is needed but HTTP BASIC auth fails
(password is not known and must not be known in this scenario)
* Keep behaviour of PassBasicAuth unchanged for compatibility
[1] http://docs.grafana.org/installation/configuration/#authproxy
This adds a "*" option to --email-domain to disable email validation, and this renames `--google-apps-domain` to `--email-domain` for clarity across providers
