Check shortcuts for conflicts.

def check_shortcuts(self):
        """Check shortcuts for conflicts."""
        conflicts = []
        for index, sh1 in enumerate(self.source_model.shortcuts):
            if index == len(self.source_model.shortcuts)-1:
                break
            if str(sh1.key) == '':
                continue
            for sh2 in self.source_model.shortcuts[index+1:]:
                if sh2 is sh1:
                    continue
                if str(sh2.key) == str(sh1.key) \
                   and (sh1.context == sh2.context or sh1.context == '_' or
                        sh2.context == '_'):
                    conflicts.append((sh1, sh2))
        if conflicts:
            self.parent().show_this_page.emit()
            cstr = "\n".join(['%s <---> %s' % (sh1, sh2)
                              for sh1, sh2 in conflicts])
            QMessageBox.warning(self, _("Conflicts"),
                                _("The following conflicts have been "
                                  "detected:")+"\n"+cstr, QMessageBox.Ok)