'tahoe --version[and-path]' should print versions even if a requirement check fails

[daira]

If the checks on dependencies done by check_all_requirements in src/allmydata/__init__.py​ fail, but we were trying to run tahoe --version or tahoe --version-and-path, then it would be useful to print the versions (and paths) anyway.

An acceptable way to implement this would be to always print the versions and paths whenever the requirements check fails, regardless of what command we were trying to run.