added $ for oids

lib/pure/oids.nim

@@ -1,7 +1,7 @@
 #
 #
 #            Nimrod's Runtime Library
-#        (c) Copyright 2012 Andreas Rumpf
+#        (c) Copyright 2013 Andreas Rumpf
 #
 #    See the file "copying.txt", included in this
 #    distribution, for details about the copyright.
@@ -52,6 +52,10 @@ proc oidToString*(oid: TOid, str: cstring) =
     inc(i)
   str[24] = '\0'
 
+proc `$`*(oid: TOid): string =
+  result = newString(25)
+  oidToString(oid, result)
+
 var
   incr: int 
   fuzz: int32