Avoid shadowing `exec.Command` errors

[mislav]

Before:

• The underlying cmd.Start() error was not reported in the wrapped error message
• The error from cmd.Wait() was swallowed
• The presence of stderr output was interpreted as command failure
• execabs package was used for security

Now:

• Start() + Wait() are replaced with cmd.Run()
• The Run() error is wrapped but not swallowed
• Process exit status is used as indicator of failure instead of the contents of stderr
• safeexec package is used to allow relative PATH entries

[codecov[bot]]

Codecov Report

Merging #61 (babaa6c) into main (f8f0187) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #61   +/-   ##
=======================================
  Coverage   89.24%   89.24%           
=======================================
  Files           3        3           
  Lines         586      586           
=======================================
  Hits          523      523           
  Misses         48       48           
  Partials       15       15           

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update f8f0187...babaa6c. Read the comment docs.

[seachicken]

It's nice that it works even if we have .\git.bat in the directory. https://github.com/golang/go/issues/43724#issuecomment-763734001 Thank you!

[mislav]

You're welcome! This allows me to use gh poi in the GitHub CLI repository, where I have a local bin/gh executable and my PATH set up to include ./bin. Before, gh poi mysteriously failed because the execabs error was swallowed 😅