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Merge pull request #136 from mdboom/sort-benchmark-labels

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Fix #138: Don't install tests.
Fix the displaying of stderr
Merge pull request #141 from mdboom/dont-install-tests

Don't install tests.
Store stderr from failing tests in results (might be useful someday)
Save errcode as well.
Merge pull request #146 from mdboom/fix-stderr-display

Fix the displaying of stderr
Don't display error from Conda matching
Support all environment plugins in the `--python` argument
Fix range_spec check
Don't have Conda do any network fetching
Handle "same" in the plugin.