* Replace pipes.quote for shlex_quote
* More migration of pipes.quote to shlex_quote
Note that we cannot yet move module code over. Modules have six-1.4
bundled which does not have shlex_quote. This shouldn't be a problem as
the function is still importable from pipes.quote. It's just that this
has become an implementation detail that makes us want to import from
shlex instead.
Once we get rid of the python2.4 dependency we can update to a newer
version of bundled six module-side and then we're free to use
shlex_quote everywhere.
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