Don't allow trailing metadata from the client.

	Change on 2014/12/19 by ctiller <ctiller@google.com>
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=82527952

src/core/surface/call.c

@@ -296,8 +296,14 @@ grpc_call_error grpc_call_add_metadata(grpc_call *call, grpc_metadata *metadata,
   grpc_call_element *elem;
   grpc_call_op op;
 
-  if (call->state >= CALL_FINISHED) {
-    return GRPC_CALL_ERROR_ALREADY_FINISHED;
+  if (call->is_client) {
+    if (call->state >= CALL_STARTED) {
+      return GRPC_CALL_ERROR_ALREADY_INVOKED;
+    }
+  } else {
+    if (call->state >= CALL_FINISHED) {
+      return GRPC_CALL_ERROR_ALREADY_FINISHED;
+    }
   }
 
   op.type = GRPC_SEND_METADATA;