Improve the detection of undefined variables in function arguments

This patch involves a lot of subtle changes:

* is_defined_before takes in consideration the fact that its argument
  node is a default value for a Lambda / Function.
  If it is a default value, then the search is left to the parent of
  the lambda. Basically for x in the following, the result of is_defined_before
  will be determined by foo:

  def foo():
      x = 42
      func = lambda x=x: x * x
      return func

* there's another special rule for undefined-variable which verifies that
  a node is used in Arguments.defaults and if the actual definition
  is happening before the Arguments statement, basically trying
  to understand the following:

  class A:
     x = 42
     foo = lambda x=x: x * x

* undefined variable is emitted if both scope types, for the node
  analyzed and for its actual definition, is they are both lambda
  scopes.

Closes issue #404.

1 files changed, 1 insertions, 1 deletions

diff --git a/ChangeLog b/ChangeLog
index d4a126d..f7a02a7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -118,7 +118,7 @@ ChangeLog for Pylint
     * Improve the detection of undefined variables and variables used before
       assignment for variables used as default arguments to function,
       where the variable was first defined in the class scope.
-      Closes issue #342.
+      Closes issue #342 and issue #404.
 
 
 2015-03-14 -- 1.4.3