runtest.py: Simplify test discovery code (and show where unittests are)
runtest.py: Remove double check if no tests are found.
Make runner for unit tests configurable, add TAPTestRunner that formats
output according to TAP protocol http://testanything.org/

    runtest.py --runner TestUnit.TAPTestRunner src\engine\SCons\ActionTests.py
runtest.py: Make sure --runner argument is only passed to unit tests
Switch unit tests to configurable runner
Fix invokation for two unusual tests
Fix test runner invokation for Tool/javacTests.py
Fix test runner invokation for src/engine/SCons/Tool/msvsTests.py
Fix running tests in subdir as argument to runtest.py, e.g.

    python runtest.py test/CC
Add test for "runtest test/somedir" case
Merged in techtonik/scons (pull request #124)

New configurable test runner for unittests
rpm tool: get default rpm arch more robustly, from rpm itself.