account_budget has UnicodeEncodeError when raising except_osv

[Sandy Carter (http://www.savoirfairelinux.com)]

Invoice budget's warning when crossovered budget lines are not related to any account will cause a UnicodeEncodeError if the account has unicode-only characters such as é.

How to reproduce:
* Fresh database, install account_budget without demo.
* Under menu (Invoicing|Budgets|Budgets)
** Create a new budget, name it what you want, add the dates and code you want.
** Add a budget line, choose whatever dates you want and add a new budgetary position by clicking Create and Edit.
*** In the Budgetary Position form, put whatever code you want, but Give it a name with a utf character such as "Testé".
*** Do not add an account to the budgetary position.
*** Save the budgetary position
** Save and close the budgetary line
* Save the Budget form

Expected output:
OpenERP outputs a Warning (except_osv) which reads:
Error!

The Budget 'Testé' has no accounts!

Actual output:
OpenERP outputs an error message with the following output

Server Traceback (most recent call last):
  File "web/addons/web/session.py", line 89, in send
    return openerp.netsvc.dispatch_rpc(service_name, method, args)
  File "openerp/netsvc.py", line 358, in dispatch_rpc
    result = ExportService.getService(service_name).dispatch(method, params)
  File "openerp/service/web_services.py", line 626, in dispatch
    res = fn(db, uid, *params)
  File "openerp/osv/osv.py", line 190, in execute_kw
    return self.execute(db, uid, obj, method, *args, **kw or {})
  File "openerp/osv/osv.py", line 132, in wrapper
    return f(self, dbname, *args, **kwargs)
  File "openerp/osv/osv.py", line 199, in execute
    res = self.execute_cr(cr, uid, obj, method, *args, **kw)
  File "openerp/osv/osv.py", line 187, in execute_cr
    return getattr(object, method)(cr, uid, *args, **kw)
  File "server/openerp/osv/orm.py", line 3674, in read
    result = self._read_flat(cr, user, select, fields, context, load)
  File "openerp/osv/orm.py", line 3795, in _read_flat
    res2 = self._columns[f].get(cr, self, ids, f, user, context=context, values=res)
  File "openerp/osv/fields.py", line 1142, in get
    result = self._fnct(obj, cr, uid, ids, name, self._arg, context)
  File "account_budget/account_budget.py", line 139, in _prac
    res[line.id] = self._prac_amt(cr, uid, [line.id], context=context)[line.id]
  File "account_budget/account_budget.py", line 119, in _prac_amt
    raise osv.except_osv(_('Error!'),_("The Budget '%s' has no accounts!") % str(line.general_budget_id.name))
UnicodeEncodeError: 'ascii' codec can't encode character u'\xe9' in position 4: ordinal not in range(128)

Version 7.0
addons: r9900
server: r5259
web: 4159