Install python-magic (it helps s3cmd) and a convenience /src symlink

Dockerfile

@@ -21,6 +21,7 @@ run	apt-get install -y -q reprepro
 # Install s3cmd 1.0.1 (earlier versions don't support env variables in the config)
 run	apt-get install -y -q python-pip
 run	pip install s3cmd
+run	pip install python-magic
 run	/bin/echo -e '[default]\naccess_key=$AWS_ACCESS_KEY\nsecret_key=$AWS_SECRET_KEY\n' > /.s3cfg
 # Download dependencies
 run	PKG=github.com/kr/pty REV=27435c699;		 git clone http://$PKG /go/src/$PKG && cd /go/src/$PKG && git checkout -f $REV
@@ -32,6 +33,7 @@ run	apt-get install -y -q mercurial
 run	PKG=code.google.com/p/go.net/ REV=84a4013f96e0;  hg  clone http://$PKG /go/src/$PKG && cd /go/src/$PKG && hg  checkout    $REV
 # Upload docker source
 add	.       /go/src/github.com/dotcloud/docker
+run	ln -s	/go/src/github.com/dotcloud/docker /src
 # Build the binary
 run	cd /go/src/github.com/dotcloud/docker && ./make.sh
 cmd	cd /go/src/github.com/dotcloud/docker && ./release.sh