After recent changes, '--foo bar' was working, but '--foo=bar' was not. The
test had a typo (?) (bar != baz) and because util.argparse is not strict by
default, the typo was not caught.
The typo caused the code to take a different path, and bypassed the buggy
handling of --foo=bar options.
I've preserved the existing test (typo and all!) because it's still an
interesting test, and ensures no unintended behaviour changes compared to the
old code.
However I've added a new variant of the test, with strict mode enabled and the
typo fixed. This test failed due to the bug, and this commit introduces a fix.
The second return value is (not insensibly) assumed to be an error. Instead of
returning a value there in the success case, copy the positional arguments
into the existing opts table.