with ``{x,y}`` generative syntax.  Thanks Andrew Pashkin.

Make substitution engine ignore factor arrays, fix #302

The fix assumes, that the bug was that the substitution engine -
tox.config.Replacer, while recursvely replacing references to actual
values, treated factor arrays (like {py27,py34}) as references, that
are needed to be replaced, which they are not.

The patch simply amends regex which is used by Replacer to recognize
references, to ignore factor arrays. And factor arrays assumed to be
values, enclosed in curly braces, that contain at least one comma.

to "pip freeze" to obtain the list of installed packages.
Thanks Ted Shaw, Holger Krekel.
close issue66: add documentation to jenkins page on how to avoid
"too long shebang" lines when calling pip from tox.  Note that we
can not use "python -m pip install X" by default because the latter
adds the CWD and pip will think X is installed if it is there.
"pip install X" does not do that.

(experimental) New feature: When a search for a config file fails, tox tries loading