Change buildslave's testPunctuation to not depend on the platform

As a side effect, it now effectively checks that individual arguments are
passed properly, instead of just verifying their concatenation.
Merge testMultiWordCommand and testPunctuation into a single test

Since they're about the same thing, really.
Update docker tutorial to use standard install procedure

 * Use the standard installation instruction instead of the master
   version: 0.7 has been out for some time now.
 * As a result, switch to `sudo docker` instead of `sudo ./docker`.
 * Correct minor typos
Merge pull request #1248 from pquentin/docker-doc

Update docker tutorial
Merge pull request #1245 from SpecLad/punct+

Change buildslave's testPunctuation to not depend on the platform
re-raise the original exception when cleaning the database

This ensures we get a full traceback from the point where that exception
was raised.
fix pyflake