fix string range to have full unicode range (up to 10FFFF).
add test for string range.

test has minor failure: after loop the index == len(s); should be len(s)-1
in this case.  according to spec, vars are left at position at last
iteration.

R=ken,rsc
DELTA=259  (161 added, 96 deleted, 2 changed)
OCL=27343
CL=27343
diff --git a/src/runtime/runtime.h b/src/runtime/runtime.h
index bdadbfc..6b398c2 100644
--- a/src/runtime/runtime.h
+++ b/src/runtime/runtime.h
@@ -272,6 +272,7 @@
 int32	findnull(byte*);
 void	dump(byte*, int32);
 int32	runetochar(byte*, int32);
+int32	charntorune(int32*, uint8*, int32);
 
 /*
  * very low level c-called