This canonicalizes paths and urls as early as possible so we don't
have to remember to do it at the point of use. It will fix a swath
of SVN 1.7 problems in one go.
Its ok to double canonicalize things.
SVN 1.7 still fails, still not worrying about that.
[ew: commit title]
Signed-off-by: Eric Wong <normalperson@yhbt.net>