* Use RequestURI when redirecting to canonical path.
Caddy may trim a request's URL path when it starts with the path that's
associated with the virtual host. This change uses the path from the request's
RequestURI when performing a redirect.
Fix issue #1327.
* Rename redirurl to redirURL.
* Redirect to the full URL.
The scheme and host from the virtual host's site configuration is used
in order to redirect to the full URL.
* Add comment and remove redundant check.
* Store the original URL path in request context.
By storing the original URL path as a value in the request context,
middlewares can access both it and the sanitized path. The default
default FileServer handler will use the original URL on redirects.
* Replace contextKey type with CtxKey.
In addition to moving the CtxKey definition to the caddy package, this
change updates the CtxKey references in the httpserver, fastcgi, and
basicauth packages.
* httpserver: Fix reference to CtxKey