add syntax highlighting for self in python2

syntax/python.vim

 syn keyword pythonStatement     exec return
 syn keyword pythonStatement     pass raise
 syn keyword pythonStatement     global assert
-syn keyword pythonStatement     lambda
+syn keyword pythonStatement     lambda 
 syn keyword pythonStatement     with
 syn keyword pythonStatement     def class nextgroup=pythonFunction skipwhite
 syn keyword pythonRepeat        for while
   if !s:Enabled("g:python_print_as_function")
     syn keyword pythonStatement  print
   endif
-  syn keyword pythonImport      as
+  syn keyword pythonImport      as self
   syn match   pythonFunction    "[a-zA-Z_][a-zA-Z0-9_]*" display contained
 else
   syn keyword pythonStatement   as nonlocal None