Added a 'glob' command to the slave.

Can be used to retrieve a list of files from the slave that match
a given pattern. (This is somewhat more portable than using shell
expansion.)
Custom steps can use this command to add filenames to a property
of the build where they may be later picked up by an uploading step.

RemoteCommand('glob', dict(path='[Bb]uild[Bb]ot-*', workdir='wkdir'))
pep8 (so close)
Merge branch 'slave-fs-cmds-cleanup' into slave-glob-command

* slave-fs-cmds-cleanup: (148 commits)
  removed blank line
  send headers and errno for failed fs commands
  check rc in a callback (errback is not called)
  Fix failing test & shell command
  update steps to use requiredArgs
  replace assertions, raise ValueError instead
  replaced "except as" syntax w/ 2.4 compatible comma syntax
  Removed bare excepts
  apply 09749e7 to master
  On solaris use the tail in /usr/xpg4/bin/tail insteaf of /usr/bin/tail which does not support the -n option
  Do not catch GeneratorExit exception
  remove use of MutableMapping, not in Python 2.5
  Ignore decoding errors in atom/rss feeds; fixes #951
  Fix step None bug
  sphinx doesn't seem to support relative paths for logos anymore
  fix typo in comment
  Add systemd unit for slave.
  Add systemd service unit for master.
  add whitespace to avoid failure with Sphinx-1.2.1
  Fix failures where 'git clean' fails but could be clobbered
  ...
Incorporate improvements from #1066

* rename sent updates `glob` -> `files` (as in ListDir)
* drop the asserts, use base.Command.requiredArgs
* catch only OSError (even that one is quite unlikely to appear) and
  send the appropriate `rc` to master
* rename `globpath` -> `globname` (as in the python docs:
  http://docs.python.org/2/library/glob.html)
Added relnote, developer doc
Added runGlob to CompositeStepMixin
Mention CompositeStepMixin.runGlob in relnotes
Added manual/docs, fixed reference in releasenotes
Merge jpommerening/buildbot:slave-glob-command (PR #970)

+autopep8