Previously directories have been merely pulled to the front, and then
sorted arbitrarily. That is, their order among themselves depended on
the filesystem implementations. Something opaque to the visitor.
This fixes said inconsistency, and implements the by-size-then-by-name
order I initially intended for this.
* Use helper functions in staticfiles to redirect.
Previously the browse package invoked staticfiles.Redirect when
redirecting clients who requested a directory but with a Request-URI
that did not contain a trailing '/'. staticfiles.Redirect only used a
relative URI. This change defers the decision of how to format the
Location header value to the helper methods in the staticfiles package.
* Update const URLPathCtxKey in browse package.
