[IMP] fields: reduce verbosity of debug log for registry loading

This log line is only useful when debugging registry
loading, a limited use case now that Odoo 8 is stable.
It makes the debug log more difficult to read and causes
a small performance penalty when debug[_rpc] is on.
(+0.2s i.e. 10% extra time for loading a registry with 47
modules on a core i5-4200U machine)

openerp/fields.py

@@ -638,7 +638,7 @@ class Field(object):
         assert self.store or self.column
 
         # determine column parameters
-        _logger.debug("Create fields._column for Field %s", self)
+        #_logger.debug("Create fields._column for Field %s", self)
         args = {}
         for attr, prop in self.column_attrs:
             args[attr] = getattr(self, prop)