Added a tutorial note and example regarding the scope of loop variables in a list comprehension.  Includes a justification and a comparision to regular for-loops.
Added a tutorial note and example regarding the scope of loop variables
in a list comprehension.  Includes a justification and a comparision
to regular for-loops.

Closes SF bug 605047.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator