URL: return error on malformed URLs with junk after port number

... because it causes confusion with users. Example URLs:

"http://[127.0.0.1]:11211:80" which a lot of languages' URL parsers will
parse and claim uses port number 80, while libcurl would use port number
11211.

"http://user@example.com:80@localhost" which by the WHATWG URL spec will
be treated to contain user name 'user@example.com' but according to
RFC3986 is user name 'user' for the host 'example.com' and then port 80
is followed by "@localhost"

Both these formats are now rejected, and verified so in test 1260.

Reported-by: Orange Tsai