Support in-place upgrades of new minio binary and releases. (#4961)

This PR allows 'minio update' to not only shows update banner
but also allows for in-place upgrades.

Updates are done safely by validating the downloaded
sha256 of the binary.

Fixes #4781

vendor/github.com/inconshreveable/go-update/patcher.go

@@ -0,0 +1,24 @@
+package update
+
+import (
+	"io"
+
+	"github.com/inconshreveable/go-update/internal/binarydist"
+)
+
+// Patcher defines an interface for applying binary patches to an old item to get an updated item.
+type Patcher interface {
+	Patch(old io.Reader, new io.Writer, patch io.Reader) error
+}
+
+type patchFn func(io.Reader, io.Writer, io.Reader) error
+
+func (fn patchFn) Patch(old io.Reader, new io.Writer, patch io.Reader) error {
+	return fn(old, new, patch)
+}
+
+// NewBSDifferPatcher returns a new Patcher that applies binary patches using
+// the bsdiff algorithm. See http://www.daemonology.net/bsdiff/
+func NewBSDiffPatcher() Patcher {
+	return patchFn(binarydist.Patch)
+}