Added a class MallocHeapOutputBufferType for types that are passed

as &buffer, &size and allocated by the called function.

Tools/bgen/bgen/bgenHeapBuffer.py

@@ -111,3 +111,32 @@ class VarVarHeapOutputBufferType(VarHeapOutputBufferType):
 
     def passOutput(self, name):
         return "%s__out__, %s__len__, &%s__len__" % (name, name, name)
+
+class MallocHeapOutputBufferType(HeapOutputBufferType):
+    """Output buffer allocated by the called function -- passed as (&buffer, &size).
+    
+    Instantiate without parameters.
+    Call from Python without parameters.
+    """
+
+    def getargsCheck(self, name):
+        Output("%s__out__ = NULL;", name)
+
+    def getAuxDeclarations(self, name):
+        return []
+
+    def passOutput(self, name):
+        return "&%s__out__, &%s__len__" % (name, name)
+
+    def getargsFormat(self):
+        return ""
+
+    def getargsArgs(self, name):
+        return None
+
+    def mkvalueFormat(self):
+        return "z#"
+
+    def cleanup(self, name):
+        Output("if( %s__out__ ) free(%s__out__);", name, name)
+