HTTP [Pike 8.0]: Survive invalidly %-encoded requests again.
Roxen.http_decode_string() in Pike 8.0 throws errors for invalidly
Behavior is now as follows:
* Invalidly %-encoded query-variables or cookies -- assume that the
erroneous query-variable or cookie was sent unencoded.
* Invalidly %-encoded path -- generate a bad request (400) error.
Fixes [bug 7818 (#7818)].