[CMake] Inconsistent CTest/CMake variable naming

[Maik Beckmann]

Hello,

I wonder if the following name inconsistency is by intention or an oversight. 
In cmake scripts there are
  CMAKE_SOURCE_DIR
  CMAKE_BINARY_DIR
and in ctest the counterparts are called
  CTEST_SOURCE_DIRECTORY
  CTEST_BINARY_DIRECTORY
Why not
  CTEST_SOURCE_DIR
  CTEST_BINARY_DIR
??

Thanks,
 -- Maik