use table instead of local to avoid lua VM 200 variables limit.

[michaelpengcn]

No description provided.

[treert]

有bug，需要在生成.message_type = 的地方加上前缀。

has bug, need change.
add type_name = _prefix + type_name before

        if field_desc.type == FDP.TYPE_MESSAGE:
            context('.message_type = %s\n' % type_name)
        else:
            context('.enum_type = %s\n' % type_name)