[CMake] MESSAGE SEND_ERROR and FATAL_ERROR

[David Cole]

Regarding:
  ...the documentation is poor here, and I will update it once I figure 
out what to do.
  MESSAGE([SEND_ERROR|STATUS|FATAL_ERROR] "message" [NO_NEWLINE])

The first argument to MESSAGE is optional, but the documentation does 
not say which one is the default value if it is left out. Is it 
SEND_ERROR? Whoever updates the documentation should update it to state 
what the default value of the first arg is...

:-)
David