mark and sweep GC without bitvectors works

todo.txt

@@ -2,9 +2,8 @@ version 0.9.2
 =============
 
 - FFI:
-  * test libffi on windows  --> fowl
+  * test libffi on windows
   * test: times.format with the FFI
-- GC: variation of m&s GC
 - GC: implement simple generational GC
   * first version: mark black in write barrier
   * second version: introduce fake roots instead of marking black
@@ -108,7 +107,8 @@ GC
 Optimizations
 =============
 
-- optimize 'if' with a constant condition
+- optimize 'if' with a constant condition --> necessary in frontend for better
+  dead code elimination
 - escape analysis for string/seq seems to be easy to do too;
   even further write barrier specialization
 - inlining of first class functions