vendor: add sourcegraph/s3cache and dependencies

Adds:
 - github.com/kr/http/transport
 - github.com/sqs/s3
 - github.com/sqs/s3/s3util
 - sourcegraph.com/sourcegraph/s3cache

vendor/github.com/sqs/s3/s3util/config.go

@@ -0,0 +1,28 @@
+// Package s3util provides streaming transfers to and from Amazon S3.
+//
+// To use it, open or create an S3 object, read or write data,
+// and close the object.
+//
+// You must assign valid credentials to DefaultConfig.Keys before using
+// DefaultConfig. Be sure to close an io.WriteCloser returned by this package,
+// to flush buffers and complete the multipart upload process.
+package s3util
+
+// TODO(kr): parse error responses; return structured data
+
+import (
+	"net/http"
+
+	"github.com/sqs/s3"
+)
+
+var DefaultConfig = &Config{
+	Service: s3.DefaultService,
+	Keys:    new(s3.Keys),
+}
+
+type Config struct {
+	*s3.Service
+	*s3.Keys
+	*http.Client // if nil, uses http.DefaultClient
+}