string-hash and string-ci-hash now return nonnegative fixnums only.

scheme/last-revision

@@ -1 +1 @@
-1847
+1848

src/ikarus-symbol-table.c

@@ -52,7 +52,7 @@ compute_hash(ikptr str){
   h = h + (h << 3);
   h = h ^ (h >> 11);
   h = h + (h << 15);
-  return h;
+  return (h >= 0) ? h : (1 - h);
 }
 
 ikptr