Allows you to avoid the `Keg::ConflictError` recommending that you invoke `brew link --overwrite` in scenarios when you know that that's how you'd proceed anyway.
There's a few bits of functionality that Homebrew has changed over the
years, makes sense as a sensible default but some people find really
annoying:
- automatically running `brew update`
- automatically running `brew cleanup`
- automatically upgrading outdated dependents
- automatically reinstalling broken dependents
For each of these: let's improve the documentation of the commands
whose behaviour is changed and the environment variables themselves.
Otherwise if there's no search results then there's no indication what
was being searched for:
```
==> Searching for similarly named formulae...
Error: No similarly named formulae found.
==> Searching for a previously deleted formula (in the last month)...
Error: No previously deleted formula found.
==> Searching taps on GitHub...
Error: No formulae found in taps.
```
- Suppress (some more) warnings when doing `brew install --quiet`
- Clarify `man brew` output that we don't suppress all warnings
for all commands with `--quiet`
While I was doing this I noticed references to the (soon to be
deprecated) `brew switch` so:
- remove these references in `install` output
- remove a reference in the documentation
- add a comment to remind me to deprecate `brew diy`, too
Fixes#9179
- Run `brew search` for local formulae first (as it's quickest) rather
than checking Git history.
- Don't output `Searching taps...` because `Searching taps on GitHub...`
is output by the called function (and because it'll say it's searching
taps even when it is not if `HOMEBREW_NO_GITHUB_API` is set).
