1. Support for showing line numbers when debugging ctest --show-line-numbers
2. Modify the ctest initialization code, so that it can be delayed
3. Handlers now have corresponding command if they were invoked from the command (so far only update actually use that)
4. Start command is simplified and the functionality is moved to CTest
5. Update can perform initial checkout if CTEST_CHECKOUT_COMMAND is set
6. Add test that checks out kwsys and perform tests on the fresh checkout

ENH: Improve internal test handling by creating a test class. Command cmEnableTesting now only sets CMAKE_TESTING_ENABLED and cmAddTest only adds a test to the list. The actual test files are written by local generator. This way we can at some point in the future replace DartTestfile with some XML file