[Gc] GC_is_disabled returns false when GC_enable() is called too many times.

[Kjetil Matheussen]

...which is quite confusing. Perhaps GC_is_disabled should be changed 
like this?


[kjetil at ttlush gc-7.2]$ diff -u misc_bu.c misc.c
--- misc_bu.c	2012-12-09 14:18:53.185065422 +0100
+++ misc.c	2012-12-09 14:20:33.955746560 +0100
@@ -1472,7 +1472,7 @@

  GC_API int GC_CALL GC_is_disabled(void)
  {
-    return GC_dont_gc != 0;
+    return GC_dont_gc >= 0;
  }

  /* Helper procedures for new kind creation.     */