Create a separate space for global property cells

src/globals.h

Index: src/globals.h
===================================================================
--- src/globals.h	(revision 2321)
+++ src/globals.h	(working copy)
@@ -261,11 +261,12 @@
   OLD_DATA_SPACE,     // May not have pointers to new space.
   CODE_SPACE,         // Also one of the old spaces.  Marked executable.
   MAP_SPACE,          // Only map objects.
+  GLOBAL_PROPERTY_CELL_SPACE,  // Only global property cell objects.
   LO_SPACE,           // Large objects.
   FIRST_SPACE = NEW_SPACE,
-  LAST_SPACE = LO_SPACE  // <= 5 (see kSpaceBits and kLOSpacePointer)
+  LAST_SPACE = LO_SPACE  // <= 9 (see kSpaceBits and kLOSpacePointer)
 };
-const int kSpaceTagSize = 3;
+const int kSpaceTagSize = 4;
 const int kSpaceTagMask = (1 << kSpaceTagSize) - 1;