[vala] method: Always consider compatible with itself

[Rico Tzschichholz <ricotz src gnome org>]

commit c0ff1adfb3c96c2effddadbae441ab2a81cb0751
Author: Marvin W <git larma de>
Date:   Mon Mar 20 18:50:06 2017 +0100

    method: Always consider compatible with itself
    
    This is even the case with unresolved types.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=773135

 vala/valamethod.vala |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/vala/valamethod.vala b/vala/valamethod.vala
index f79ec7b..8789468 100644
--- a/vala/valamethod.vala
+++ b/vala/valamethod.vala
@@ -307,6 +307,12 @@ public class Vala.Method : Subroutine, Callable {
         * @return true if the specified method is compatible to this method
         */
        public bool compatible (Method base_method, out string? invalid_match) {
+               // method is always compatible to itself
+               if (this == base_method) {
+                       invalid_match = null;
+                       return true;
+               }
+
                if (binding != base_method.binding) {
                        invalid_match = "incompatible binding";
                        return false;