added the flag traceback.limit that allow to limit the size of the stack trace.

theano/configdefaults.py

@@ -68,3 +68,7 @@ AddConfigVar('gpuelemwise.sync',
 AddConfigVar('cmodule.mac_framework_link',
         "If set to true, breaks certain mac installations with the infamous Bus Error",
         BoolParam(False))
+
+AddConfigVar('traceback.limit',
+             "The number of stack to trace. 0 mean all.",
+             IntParam(0))

theano/gof/op.py

@@ -319,7 +319,9 @@ class PureOp(object):
 
         """
         node = self.make_node(*inputs, **kwargs)
-        node.tag.trace = traceback.extract_stack()[:-1]
+        limit = theano.config.traceback.limit
+        if limit == 0: limit = None
+        node.tag.trace = traceback.extract_stack(limit=limit)[:-1]
         if self.default_output is not None:
             return node.outputs[self.default_output]
         else:

theano/gof/type.py

@@ -245,7 +245,9 @@ class PureType(object):
 
         """
         r = self.make_variable(name)
-        r.tag.trace = traceback.extract_stack()[:-1]
+        if limit == 0: limit = None
+        node.tag.trace = traceback.extract_stack(limit=limit)[:-1]
+        r.tag.trace = traceback.extract_stack(limit)[:-1]
         return r
 
     def values_eq(self, a, b):