url: treat \ the same as /

See https://code.google.com/p/chromium/issues/detail?id=25916

Parse URLs with backslashes the same as web browsers, by replacing all
backslashes with forward slashes, except those that occur after the
first # character.

Manual rebase of 9520ade

Signed-off-by: Trevor Norris <trev.norris@gmail.com>