Updated RFM12B example sketches to use accessor functions

Fixed typo in RFM12B_Struct_node that prevents compilation.
Changed all RFM12B example sketches to use accessor functions rather than accessing Data and DataLen directly.
Changed all RFM12B example sketches to use do{}while instead of while{} when waiting for ACK.

Validated that all example sketches compile.

Tested that the following sketches work in a pure RFM12B environment.  (I have no flash in my set up.  Sketches that rely on flash were not tested.  Sketches that access flash but do not rely on it had the flash statements commented out for the test.)
    LED_Control_Gateway
    LED_Control_Node
    RFM12B_Struct_gateway
    RFM12B_Struct_node
    Receive
    Send
    Test_2way_gateway
    Test_2way_node

Thanks again for creating the compatibility changes.  This is a great enabler for those of us with mixed environments!
  - Chip