Releng: Update to Tycho-0.23.1 for bz 459873, Unify Target Platforms

- Tycho-0.23 makes multiple Hudson builds in parallel more robust
- Use SWTbot-2.2.1 on Eclipse-3.8 to keep target dependencies clean
- Bring *.target files in sync with pom-config.xml for interactive use
- Align .gitignore with TCF's .gitignore

Change-Id: I6dfd7bfee43e8fcab1b6e7aae7a0b46f2f83bbf4
Signed-off-by: Martin Oberhuber <mober.at+eclipse@gmail.com>