try to make callframe().my.<$x> read-only

It doesn't quite work, but it reduces the amount of damage
you can do to the caller's lexpad

Also run new callframe.t

src/core/LexPad.pm

@@ -4,7 +4,7 @@ class LexPad is Associative {
 
     multi method postcircumfix:<{ }>($thing) {
         Q:PIR {
-            .local pmc key
+            .local pmc key, false
             key = find_lex '$thing'
             $P0 = find_lex 'self'
             $P1 = getattribute $P0, '$!parrot_lexpad'
@@ -13,6 +13,9 @@ class LexPad is Associative {
             unless null %r goto done
             %r = get_hll_global 'Mu'
           done:
+            %r = clone %r
+            false = get_hll_global 'False'
+            setprop %r, 'rw', false
         }
     }
 

t/spectest.data

@@ -315,6 +315,7 @@ S05-substitution/match.t
 S05-substitution/subst.t
 S05-transliteration/trans.t
 # S05-transliteration/with-closure.t
+S06-advanced_subroutine_features/callframe.t
 S06-advanced_subroutine_features/lexical-subs.t
 S06-advanced_subroutine_features/recurse.t
 S06-advanced_subroutine_features/return.t