Support authenticated proxy URLs

[egao1980]

Quicklisp bootstrap parse-url supports http://user:password@proxy:port URL scheme but the client code doesn't. We can just port the exising functions across the projects.

(ql-http:parse-urlstring "http://username:password@proxyhost:8080")

0: ((LABELS QL-HTTP::IN-PORT :IN QL-HTTP::PARSE-URLSTRING) #\R)
Locals:
CHAR = #\R
1: (QL-HTTP::PARSE-URLSTRING "http://username:password@proxyhost:8080")

[tamurashingo]

Hi.
PR is already exists. #80

Apply this patch to your local quicklisp, you can use new parse-url.