Add warning/error handlin for problematic nested scopes cases as described in PEP 227. symtable_check_unoptimized() warns about import * and exec with "in" when it is used in a function that contains a nested function with free variables. Warnings are issued unless nested scopes are in effect, in which case these are SyntaxErrors. symtable_check_shadow() warns about assignments in a function scope that shadow free variables defined in a nested scope. This will always generate a warning -- and will behave differently with nested scopes than without. Restore full checking for free vars in children, even when nested scopes are not enabled. This is needed to support warnings for shadowing. Change symtable_warn() to return an int-- the return value of PyErr_WarnExplicit. Sundry cleanup: Remove commented out code. Break long lines.