Works around Rubycop not liking method names that start with `is_`
by changing convention from singular to plural.

I think it's better that way anyway.

Suggested in #1084.

Made the existing warning output entirely to STDERR, because
previously the first line went to STDERR and subsequent ones went
to STDOUT.

formula_versions: fix erroneous :stable in version_attributes_map

cc: Add -frounding-math to list of ignored flags

keg: don't rely on #to_formula

It doesn't always work.
For example, a keg could have been installed with a formula from a
URL, which Homebrew now does not know how to access.

Fixes #1496.

audit: fix "version should not decrease" check.

Fix the "version should not decrease" check so it correctly handles
`version_scheme`s.

Fixes #1489.

Update macOS Xcode tool checks do use Version class for comparisons

Invalid build option warnings - supersedes #1088

Filter formula build options based on those that exist.

diagnostic: skip xcode-select check with no Xcode.

If `--with-foo` is provided to a formula through a tab or through
another formula depending on it and this option does not exist it
should be filtered. If it is not (the prior behaviour) then this can
prevent bottles being used unnecessarily.

Fixes #1399.

Skip the `xcode-select` configuration check if there's no CLT or Xcode
installed as in that case neither will be used.

Fixes #1055.

Typo: delet -> delete

Check the lock directory is writable.

formulary: don't warn on old formula name from keg/rack.

brew-cask tests never fail on BrewTestBot

`brew cask-tests` collected the test results in an improper way so that it reports a false success in certain situations.
Specially, the session under BrewTestBot always reports success regardless of the test status.
With this update, the exit code of `brew cask-tests` is 1 when the test fails, and then CI preperly works.

And, if it isn't, print more helpful debugging messages.

Fixes #1456.

If there’s an old installation of e.g. `apple-gcc42` from when it was
part of `homebrew/core` then the tab will say it was from the
`homebrew/core` tap and then we’ll complain at the user (see #1459 for
an example). Instead, we only want to complain when the user actually
types in `homebrew/core/apple-gcc42` into a `brew` command.

Closes #1459.

uninstall: don't need kegs to exist for --force.

Otherwise there's an error which is a regression on previous
functionality. This mirrors `rm -f` which doesn't fail if a file doesn't
exist.

Fix `Hbc::Locations` in tests.

Support `SUDO_ASKPASS` environment variable in `brew cask`.

uninstall: refuse when dependents still installed

`brew doctor` recommends using cask to upgrade XQuartz

vendor: Update ruby-macho to 0.2.6.

brew.rb: don't exit when failing to set devcmdrun.