remove/conditionalize "shutilwhich" dependency

[warner]

Somewhere in the 1.12 development cycle, _auto_deps.py acquired an unconditional dependency upon a package named shutilwhich. This impacts downstream packagers (i.e. it isn't in Debian yet). Looking at the code, it seems that shutilwhich is only used by the integration tests, and thus should probably be moved into the [test] clause of setup.py's extras_require=. That would let non-testing downstream packages omit the dependency.

[cypher]

Twisted has a which() in twisted.python.procutils that could be used in place of shutilwhich (though it returns a list of filepaths):

​https://twistedmatrix.com/documents/current/api/twisted.python.procutils.html

For simplicity's sake, it might be better to just use that instead.

[Brian Warner <warner@…>]

In 79ff7ae/trunk:

move 'shutilwhich' dependency out to the [test] extra

This is only used by integration/conftest.py, so we don't need an
unconditional dependency on it.

closes ticket:2856

[warner]

oh, let's leave this open (but pushed out of the 1.12.1 milestone), to get that shutilwhich replaced by a normal twisted procutils.which (which we're already using in allmydata.util.iputil to find ifconfig-like programs).

[warner]

I'll point this ticket at meejah, as he wrote integration/conftest.py that uses it

[dawuud]

​https://github.com/tahoe-lafs/tahoe-lafs/pull/393

[David Stainton <dstainton415@…>]

In 805be64/trunk:

Use which from twisted

fixes #2856