Allow lenient parsing of query parameters containing = characters

In the wild many URLs are not correctly URL encoded.  As much as it's nice to write to the standard, coping with real-life URLs is important.
A common example is the padding at the end of a base64-encoded value  e.g.  "x=1&y=W253f4==&y=3"
This change makes the query string parsing more lenient by not insisting that the value of any query parameter does not contain =.
Other similarly malformed URLs could probably be handled too but this one form I've come across a few times recently.
The fix is particularly simple and seems totally safe.