- assign id for MSP_PRIVATE message with no code for the moment
- range [50-99] won't be used in multiwii and can therefore be used for any custom fork implementation without the risk of conflict id later

git-svn-id: http://multiwii.googlecode.com/svn/trunk/MultiWii_shared@1661 02679b44-d973-9852-f2fa-63770883b36c