Added a "nitpick_maybe" symbol, which is used by Nitpick. This will go away once Nitpick is part of HOL.

--- a/src/HOL/HOL.thy	Thu Mar 05 10:19:51 2009 +0100
+++ b/src/HOL/HOL.thy	Fri Mar 06 15:31:07 2009 +0100
@@ -1706,7 +1706,11 @@
 *}
 
 
-subsection {* Nitpick theorem store *}
+subsection {* Nitpick hooks *}
+
+text {* This will be relocated once Nitpick is moved to HOL. *}
+
+consts nitpick_maybe :: "'a \<Rightarrow> 'a" ("_\<^isub>?" [40] 40)
 
 ML {*
 structure Nitpick_Const_Def_Thms = NamedThmsFun