Fix special methods of class pydevd_constants.Null.
Null.__iter__() now returns an iterator for an empty tuple. The previous
implementation caused an infinite loop.
Pickling Null objects is now possible.
Fix special methods of class pydevd_constants.Null.
Don't pretend to implement special methods.
Merge branch 'akruis_fix_Null' of https://github.com/akruis/Pydev into akruis-akruis_fix_Null
Merge branch 'akruis-akruis_fix_Null' into development