URL encode the Destination: header for server side COPY

According to the documentation for object COPY:

https://developer.openstack.org/api-ref/object-store/

> Destination header string
>
> The container and object name of the destination object in the form
> of /container/object. You must UTF-8-encode and then URL-encode the
> names of the destination container and object before you include
> them in this header.

Before this patch it was not URL encoded which is out of
specification.  This causes problems doing server side copies of files
with valid URL escape codes in, (eg `%32`).

swift.go

@@ -2079,6 +2079,15 @@ func (c *Connection) ObjectUpdate(container string, objectName string, h Headers
 	return err
 }
 
+// urlPathEscape escapes URL path the in string using URL escaping rules
+//
+// This mimics url.PathEscape which only available from go 1.8
+func urlPathEscape(in string) string {
+	var u url.URL
+	u.Path = in
+	return u.String()
+}
+
 // ObjectCopy does a server side copy of an object to a new position
 //
 // All metadata is preserved.  If metadata is set in the headers then
@@ -2091,7 +2100,7 @@ func (c *Connection) ObjectUpdate(container string, objectName string, h Headers
 func (c *Connection) ObjectCopy(srcContainer string, srcObjectName string, dstContainer string, dstObjectName string, h Headers) (headers Headers, err error) {
 	// Meta stuff
 	extraHeaders := map[string]string{
-		"Destination": dstContainer + "/" + dstObjectName,
+		"Destination": urlPathEscape(dstContainer + "/" + dstObjectName),
 	}
 	for key, value := range h {
 		extraHeaders[key] = value

swift_test.go

@@ -1479,6 +1479,20 @@ func TestObjectCopy(t *testing.T) {
 	}
 }
 
+func TestObjectCopyDifficultName(t *testing.T) {
+	c, rollback := makeConnectionWithObjectHeaders(t)
+	defer rollback()
+	const dest = OBJECT + "?param %30%31%32 £100"
+	_, err := c.ObjectCopy(CONTAINER, OBJECT, CONTAINER, dest, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = c.ObjectDelete(CONTAINER, dest)
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
 func TestObjectCopyWithMetadata(t *testing.T) {
 	c, rollback := makeConnectionWithObjectHeaders(t)
 	defer rollback()