Add support for header output to LogObservers.

It turns out that this isn't necessary for anything in Buildbot, but may
be useful to users.
Remove TinderboxMailNotifier

And with it, the last ues of log.getTextWithHeaders
remove log.getTextWithHeaders
send headers in fake log files to observers, check line endings, and encode properly
header line-ending checks were too aggressive
Merge branch '9/use-data-api-3' of git://github.com/djmitche/buildbot into nine