- Extend http.URLUnescape to convert '+' to space
- Add http.URLEscape
- Rename URL.Query to EncodedQuery (and stop decoding it, as decoding this field
  before separating key/value pairs loses important information)
- Report a clean error on incomplete hex escapes
- Update existing tests, add new ones

APPROVED=rsc
DELTA=293  (256 added, 3 deleted, 34 changed)
OCL=29685
CL=29759