This will help scripts calling pysetup know if a command failed.
Printing/logging was also made more consistent, and a few things were
cleaned up. In particular, the error/Ctrl-C handling was moved from the
_run function up to the main function.
The run action is not fixed yet; it returns the dist.Distribution
instance, which is needed by test_uninstall and not trivial to fix.
“pysetup list” or “pysetup list --all” will continue to return 0 if no
distribution is found (it’s not an error), but “pysetup list
some.project” will now exit with 1 if no matching installed distribution
is found. Based on a patch by Kelsey Hightower.
This change also makes sure the logger handlers are not alterated after an
installation. That also fixes the remaining environment alteration issue in
test_packaging.