Closure inner function name conflict

[haoyu]

Theis code won't compile with current closure branch, reporting name conflict error since the two inner function f() has the same name and their C-names are not properly mangled.

def nested1():
   def f():
       def g1():
           pass

def nested2():
   def f():
       def g2():
           pass

[scoder]

Fixed as part of the class closures implementation for ticket #596:

 http://hg.cython.org/cython-devel/rev/cb1b7b395979