fixes the recently discovered GC memory leaks

This revision is intended as comparison point between the old and the new GC
The used GC can be switched in mmdisp and various statistics will be gathered during
execution (these will be removed/disabled in later revisions)

lib/system/mmdisp.nim

@@ -14,9 +14,9 @@
 {.push checks:off.}
 
 const
-  debugGC = false # we wish to debug the GC...
+  debugGC = true # we wish to debug the GC...
   logGC = false
-  traceGC = false # extensive debugging
+  traceGC = true # extensive debugging
   alwaysCycleGC = false
   alwaysGC = false # collect after every memory allocation (for debugging)
   leakDetector = false
@@ -307,7 +307,10 @@ else:
   include "system/cellsets"
   when not leakDetector:
     sysAssert(sizeof(TCell) == sizeof(TFreeCell), "sizeof TFreeCell")
-  include "system/gc"
+  when true:
+    include "system/gc"
+  else:
+    include "system/oldgc"
   
 {.pop.}