Update documentation in HOW-TO-local-git-repo, sample config

This refactors the docs since the major updates to git repo handling,
the extended builder/scheduler/etc. changes, etc.
Fix Dependent schedulers and add ForceScheduler example to sample config

Dependent schedulers must be processed after those schedulers they
depend on, since they reference the object instead of just the name.

Add ForceScheduler example to the sample config file.  This needs to
be tested.
.gitignore rotated twistd.log.* files
post-receive.py:  fix update/branch regexes; debug msgs; tweaks

- Fix new branch regular expression; was broken
- Fix update regular expression; didn't pick up some changes
- Test regex in gen_update_branch_changes
  - had a failure after a big merge; this will help debug
- Fix update regex loop logic and print out better debugging
- Other debug messages
buildsteps.sh:  runtests:  run 'realtime stop'

Clean out previous failed sessions
buildsteps.sh:  environment step:  print env; cat /etc/redhat-release
buildsteps.sh:  cosmetic tweaks

- Unset '-x' for prettier output
- Don't run 'env'; buildbot already does this
- Remove extraneous comment
Enable setting global property passthru from config

In config.yaml global section, any properties named in
'env-properties' will be passed to buildsteps.sh.

This gets some unnecessary mess out of build step configuration.
buildsteps.sh:  set runtests flavor from 'buildername' property
buildsteps.sh:  add 'ulimit -a' to step-environment()
post-receive.py:  fix update regex
buildsteps: runtests:  run 'realtime stop' *after* FLAVOR is set
buildsteps: runtests:  after environment set up, display it for debugging
Enable specifying environment variables through config

Include CCACHE_DIR example in sample config
master.cfg:  tweak debug msgs; fail on bad build step type
Add auth from reverse proxy (broken)

Authenticate from reverse proxy's basic http auth

This doesn't work with 0.8.6, but some work seems to have been done by
0.8.7, so I'm keeping it.
master.cfg no-op: better debug msgs + comments for WebStatus section
buildsteps.sh:  remove reduntand ulimit; add xenomai-git-ctl