doctor: ignore internal HOMEBREW_REPOSITORY const

...constant. Instead extract it from the brew CLI, and consider
removing it from our doctor output entirely.
doctor: ignore internal HOMEBREW_CELLAR constant

Instead extract it from the brew CLI, and consider
removing it from our doctor output entirely.
doctor: ignore internal HOMEBREW_VERSION constant

Instead extract it from the brew CLI, and consider
removing it from our doctor output entirely.
make `render_load_path` understand homebrew-fork

tweak doctor's warnings/annotations on `$LOAD_PATH` elements
Merge pull request #8221 from rolandwalker/honest_doctor_homebrew

Adjust `brew cask doctor` for homebrew-fork