Removed some unsafe uses of StringShape....

src/handles.cc

Index: src/handles.cc
===================================================================
--- src/handles.cc	(revision 694)
+++ src/handles.cc	(working copy)
@@ -217,7 +217,7 @@
 
 
 Handle<String> SubString(Handle<String> str, int start, int end) {
-  CALL_HEAP_FUNCTION(str->Slice(StringShape(*str), start, end), String);
+  CALL_HEAP_FUNCTION(str->Slice(start, end), String);
 }