Make HTMLLogFile extend LogFile.

If logfiles were pickled with the "html" property and fake an open
logfile. Allow specifying a maximum size for logfiles to be embedded
in the pickles, otherwise just use the mechanism provided by LogFile.
keep html property for small logfiles
fixed my indentation

That's it, I'll add it as a pre-commit hook
Merge branch 'master' into html-logs-in-pickles

* master: (47 commits)
  Fix docs/conf.py to work with sphinx-1.2.2
  pep8
  be sure run() returns a status and doesn't call finished or failed
  warn on use of old-style log methods in new-style steps
  prohibit use of step.step_status in new-style steps
  add step.*Statistic methods for new-style steps
  add docs for setStateStrings
  add step.setStateStrings
  backport ShellMixin and CommandMixin from nine
  cmd.add* return deferreds
  return deferreds from addHTMLLog and addURL
  return deferreds from addLog, addCompleteLog, and log.add*
  update docs for statuspng
  fix pngstatus test
  png status by revision hash
  fix pngstatus if the build is currently in progress
  Docs: add an 'import' in one spot to make the recipe easier to swallow
  fix docs regarding removal of LoggingBuildStep
  Fix w3c validator issues.
  Fix w3c validator issues.
  ...
Stub out tests
implement some tests
Store all new logs in files.

Embedding smaller logs in the pickle was a stupid idea.
fixed the cleanup-gone-wrong
Merge jpommerening/buildbot:html-logs-in-pickles (PR #1077)