[vala] Check signature of overriding methods for async

[Jürg Billeter <juergbi src gnome org>]

commit 19099dea20c20a8ec0c0aad2f9d36b94a3f61b0c
Author: Frederik 'playya' Sdun <Frederik Sdun googlemail com>
Date:   Tue Oct 13 18:34:03 2009 +0200

    Check signature of overriding methods for async
    
    Signed-off-by: Frederik 'playya' Sdun <Frederik Sdun googlemail com>

 vala/valamethod.vala |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/vala/valamethod.vala b/vala/valamethod.vala
index 8b9359a..53c842b 100644
--- a/vala/valamethod.vala
+++ b/vala/valamethod.vala
@@ -543,6 +543,10 @@ public class Vala.Method : Member {
 				return false;
 			}
 		}
+		if (base_method.coroutine != this.coroutine) {
+			invalid_match = "async mismatch";
+			return false;
+		}
 
 		return true;
 	}