localize 2 and 3 argument BUILD_SLICE...

Nontermninal name matches AST anme now. Add test.

uncompyle6/parsers/parse2.py

@@ -313,6 +313,21 @@ class Python2Parser(PythonParser):
                         "mapexpr ::= %s %s" % (opname, kvlist_n)
                     ], customize)
                 continue
+            elif opname_base == 'BUILD_SLICE':
+                slice_num  = token.attr
+                if slice_num == 2:
+                     self.add_unique_rules([
+                        'expr ::= slice2',
+                        'slice2 ::= expr expr BUILD_SLICE_2'
+                        ], customize)
+                else:
+                    assert slice_num == 3, ("BUILD_SLICE value must be 2 or 3; is %s" %
+                                            slice_num)
+                    self.add_unique_rules([
+                        'expr ::= slice3',
+                        'slice3 ::= expr expr expr BUILD_SLICE_3',
+                        ], customize)
+                continue
             elif opname_base in ('CALL_FUNCTION', 'CALL_FUNCTION_VAR',
                                  'CALL_FUNCTION_VAR_KW', 'CALL_FUNCTION_KW'):
                 args_pos = (v & 0xff)          # positional parameters