This creates command mode add_test(NAME ...). This signature is
extensible with more keyword arguments later. The main purpose is to
enable automatic replacement of target names with built target file
locations. A side effect of this feature is support for tests that only
run under specific configurations.
This moves code which generates ADD_TEST and SET_TESTS_PROPERTIES calls
into CTestTestfile.cmake files out of cmLocalGenerator and into a
cmTestGenerator class. This will allow more advanced generation without
cluttering cmLocalGenerator. The cmTestGenerator class derives from
cmScriptGenerator to get support for per-configuration script
generation (not yet enabled).