Add 3.6+ grammar for except's ending in RETURN...

Not totally out of the maze in 3.6 control flow...
There are still problems with erroneous RETURN_VALUEs becoming RETURN_END_IF,

uncompyle6/parser.py

@@ -262,6 +262,10 @@ class PythonParser(GenericASTBuilder):
         return_stmt ::= ret_expr RETURN_VALUE
         return_stmt_lambda ::= ret_expr RETURN_VALUE_LAMBDA
 
+        # return_stmts are a sequence of statements that ends in a RETURN statement.
+        # In later Python versions with jump optimization, this can cause JUMPs
+        # that would normally appear to be omitted.
+
         return_stmts ::= return_stmt
         return_stmts ::= _stmts return_stmt
 

uncompyle6/parsers/parse36.py

@@ -57,6 +57,12 @@ class Python36Parser(Python35Parser):
                             WITH_CLEANUP_FINISH END_FINALLY
 
         except_suite ::= c_stmts_opt COME_FROM POP_EXCEPT jump_except COME_FROM
+
+        # In 3.6+, A sequence of statements ending in a RETURN can cause
+        # JUMP_FORWARD END_FINALLY to be omitted from try middle
+
+        except_return ::= POP_TOP POP_TOP POP_TOP return_stmts
+        try_middle    ::= JUMP_FORWARD COME_FROM_EXCEPT except_return
         """
 
     def add_custom_rules(self, tokens, customize):

uncompyle6/scanners/scanner3.py

@@ -384,9 +384,12 @@ class Scanner3(Scanner):
                     if last_op_was_break and opname == 'CONTINUE':
                         last_op_was_break = False
                         continue
+
+            # FIXME: go over for Python 3.6+. This is sometimes wrong
             elif op == self.opc.RETURN_VALUE:
                 if inst.offset in self.return_end_ifs:
                     opname = 'RETURN_END_IF'
+
             elif inst.offset in self.load_asserts:
                 opname = 'LOAD_ASSERT'