Make `python ./setup.py trial` output friendlier if there has not been a build.

[nejucomo]

I just did this:

$ python ./setup.py trial
running update_version
git-version: wrote '1.10.0-89-gb7f3585' into 'src/allmydata/_version.py'
running trial
/home/n/virtualenvs/default/bin/python: can't open file 'bin/tahoe': [Errno 2] No such file or directory

Then I asked people in Nuts & Bolts about this and learned some details. It would be potentially helpful for other if the output instead looked like this:

$ python ./setup.py trial
running update_version
git-version: wrote '1.10.0-89-gb7f3585' into 'src/allmydata/_version.py'
running trial
Error: 'bin/tahoe' does not exist. The trial command requires tahoe to be built.

You can explicitly build tahoe by running:

$ python ./setup.py build

You can build and run trial in a single command by running:

$ python ./setup.py test

Note: The usage text already clearifies this:

$ python ./setup.py --help-commands | grep -E 'test|trial'
  test              run unit tests after in-place build
  trial             run trial (use 'bin/tahoe debug trial' for the full set of trial options)

Note: Prior to running trial, I searched in ./docs for something like testing.rst. Zooko tells me this lives on the wiki, but it seems like it should live in ./docs because it's revision specific and useful even when I'm offline.

[warner]

Milestone renamed

[warner]

setup.py trial has been removed. tox is now the recommended way to run tests, and it builds anything that's necessary. So I think this ticket is no longer relevant.