[CMake] CTEST_COMMAND ignores -j in ctest command script

[Derek Bruening]

I have a ctest command script that runs a series of builds and tests via
ctest_start(), ctest_test(), etc.  I want to run the tests in parallel by
default (I'm using cmake 2.8.0).  If I pass -j to the ctest command that
invokes the script, the tests are run in parallel:

  ctest -j5 -S /path/to/script.cmake

However if I pass the -j via CTEST_COMMAND:

  set(CTEST_COMMAND "${CTEST_EXECUTABLE_NAME} -j5")

and do not pass it in when invoking the script, the tests are not run in
parallel.  Why is that?  Is there some way to accomplish this?

- Derek