Hide these tokens to avoid malicious subprocesses e.g. sending them
over the network. Also, support using these tokens with environment
filtering and clear `HOMEBREW_PATH` from subprocesses to stop them
sniffing it. Finally, use `HOMEBREW_PATH` to detect Homebrew’s user’s
PATH for e.g. `brew doctor` etc.
If the formula's tap isn't tapped yet when running `brew pull`, a false
positive occurs for the nonstandard bump subject check, and a bogus
warning is printed, which claims the bump subject should refer to the
old version not the new version.
If we make a PR in which we're building many formulae (e.g.
https://github.com/Homebrew/homebrew-core/pull/9249) then we may want
to pull those that built and publish their bottles and discard those
that did not. Instead of saying bottles will be published when they
won't and then blowing up just avoid publishing them and print a warning
instead.
Zhiming Wang