auth v4 canonical request

[alexandre-merle]

Headers values should be trim in canonical request, like this :

GET / HTTP/1.1
Host:example.amazonaws.com
My-Header1: value1
My-Header2: "a   b   c"
X-Amz-Date:20150830T123600Z

should result in :

GET
/

host:example.amazonaws.com
my-header1:value1
my-header2:"a b c"
x-amz-date:20150830T123600Z

host;my-header1;my-header2;x-amz-date
e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855

you can notice the value of header "my-header2" was trimmed

This fix should be against rel/6.2