you can modify the code in server\openerp\tools\safe_eval.py in function safe_eval in the dictionary variable __builtins__ add:

'int':int

this is the dictionary __builtins__ to note the available functions plus int, those are the funtions that you can use in any module that use safe_eval

__builtins__ = {
            '__import__': _import,
            'True': True,
            'False': False,
            'None': None,
            'str': str,
            'globals': locals,
            'locals': locals,
            'bool': bool,
            'dict': dict,
            'list': list,
            'tuple': tuple,
            'map': map,
            'abs': abs,
            'min': min,
            'max': max,
            'reduce': reduce,
            'filter': filter,
            'round': round,
            'len': len,
            'set' : set,
            'int': int
        }

In my opinion this should be implemented in a launchpad branch as I believe int function have no security risks and is a very common function