bug in processing passwords with backslash in mail/imap proxy code

[Дениска-редиска]

Hello,

looks like there is a bug in nginx 1.8.1 in mail proxy code which used for authorization:
backslash becomes stripped from password when quoted in imap command:

* OK IMAP4 ready
p LOGIN "testdev" ",\REz=#tPc"
p NO Invalid login or password

p LOGIN "testdev" ,\REz=#tPc
p OK [CAPABILITY.....

auth_http gets following:

GET /auth HTTP/1.0
Host: 127.0.0.1
Auth-Method: plain
Auth-User: testdev
Auth-Pass: ,REz=#tPc
Auth-Protocol: imap

and 

GET /auth HTTP/1.0
Host: 127.0.0.1
Auth-Method: plain
Auth-User: testdev
Auth-Pass: ,\REz=#tPc
Auth-Protocol: imap

respectivelly
nginx conf is as following:
mail {  
  server {
        listen 127.0.0.1:143;
        server_name  mail.example.com;
        auth_http  127.0.0.1:900/auth;
        protocol   imap;
        proxy      on;
    }
}