Makefile: use 'setup.py test' for test/quicktest targets (instead of

Makefile: use 'setup.py test' for test/quicktest targets (instead of
'setup.py trial'). 'setup.py trial' clobbers the tahoe .egg's PKG-INFO
"Version:" field (resetting it to 0.0.0), possibly because it isn't invoking
the darcsver subcommand that 'setup.py test' does before it runs the 'trial'
subcommand.

This slows down quicktest by another couple of seconds (see #591) and adds
more noise to its output, but without this change, 'make test' and 'make
quicktest' fail on test_runner (which spawns bin/tahoe as a subprocess, and
with a mangled Version:, the setuptools-based entry point script refuses to
recognize our source tree as a usable version of Tahoe).