fixed PEP8 violations
added shell completion hints

For 'buildbot' and 'buildslave' subcommands that take
base directory as first argument, suggest directories.

For 'buildbot checkconfig' suggest files as first
argument.
added zsh completions files

Added files that can be used to enable tab-completion in zsh
for 'buildbot' and 'buildslave' commands.
added bash completions files

Added files that can be used to enable tab-completion in bash
for 'buildbot' and 'buildslave' commands.
SingleBranchScheduler: add createAbsoluteSourceStamps config option

This option affects multi-codebase setups. When this option is enabled,
it uses the last revision seen for each codebase without a change instead
of using the latest revision.
monkeypatch shell completions defintions for older twisted

The shell completions support was added in twisted 11.1.0. When
running with older twisted, add completions definitions we are using
to twisted.python.usage module.
Mention tab-completions in the release notes.
add missing copyright header
SingleBranchScheduler: add description and note for createAbsoluteSourceStamps argument.
SingleBranchScheduler: only access database if createAbsoluteSourceStamps enabled
SingleBranchScheduler: remove shouldntBeSet argument and return None in defer
Merge branch 'shell-completions' of git://github.com/elmirjagudin/buildbot
Add delarative configuration example in master/contrib/SimpleConfig.py
Replace monkey-patching for Twisteds without completion

This just only attempts to use usage.Completion when that attribute
exists.
Merge branch 'sbs-abs-source-stamps' of git://github.com/thedylman/buildbot
remove nonexistent sourcestamp properties

Fixes #2509.
Add comments explaining use of usage.Completions