[Cmake] BUG: multiple endifs are considered normal

[Amitha Perera]

The sequence

IF( OPENGL_glu_LIBRARY )
  MESSAGE( "OKAY" )
ENDIF( OPENGL_glu_LIBRARY )
  MESSAGE( "NOT OKAY" )
ENDIF( OPENGL_glu_LIBRARY )

will execute both message statements when the variable is set, and
only the second when the variable is not set.

(The error: the middle line should be ELSE, not ENDIF.)

Amitha.