Avoid using addresses of static variables as unique keys

The addresses of static variables may be different for different
instances of Lua, making these instances incompatible if they use
these addresses as unique keys in the registry (or other tables).

testes/db.lua

@@ -255,6 +255,10 @@ do   -- test hook presence in debug info
 end
 
 
+-- hook table has weak keys
+assert(getmetatable(debug.getregistry()._HOOKKEY).__mode == 'k')
+
+
 a = {}; L = nil
 local glob = 1
 local oldglob = glob