Only likely to kick in when environment filtering is enabled.

Otherwise we need to tediously add a dramatic number of PATHs to tests
or recurse through the runtime formulae dependencies and add all them.

CC @ilovezfs

If the formula is already installed and they've been removed: that's ok.

Fixes #2625.

The regex matches the longest possible string. Order does not matter.

This fixes an issue where audit would prompt for the creation
of an already existing versioned alias while at the same time
declaring the existing alias invalid.

Instead of trying to do this all with a single regex give up and do a
two stage process. Eventually I'll end up implementing a full ruby
parser here .

- only document HOMEBREW_* variables in the manpage (although still
  read from all the original environment variables).
- resort manpage environment variables in alphabetical order
- check the original path for trailing slashes

Added assertion to check `HOMEBREW_LOCK_DIR.stat.mode` changes after `HOMEBREW_LOCK_DIR.chmod 0555`

This may result in a slightly varied build but it’s generally just far
less annoying to be able to access all your e.g. shell configuration.

These versioned aliases don’t correspond to the correct version if not
Installed from stable.

Fixes #2596.

Check that a required versioned alias has a valid name (rather than
assuming it’s fine based on it’s existence alone) and check for
the presence of invalid version aliases.

This should handle the case where someone bumps a formula but forgets
to rename the alias that’s mentioned in #2596.

We don't care about this in external taps as this is more about code
architecture than code style.

Attempt to improve Travis CI. This time without any vendoring gems
nonsense.

This reverts commit 3e4547f5, reversing
changes made to 6edf9382.

This reverts commit 23728729, reversing
changes made to 3e4547f5.

This reverts commit 8d948e4b, reversing
changes made to 23728729.

Tweak our Travis CI configuration and the one we suggest for taps to
be faster and use caching.

If people have `HOMEBREW_RUBY_PATH` set then things explode in a rather
confusing fashion. Instead, run `bundle` for them with the arguments
that they'd want.

Also, move `macho` requires into the module itself; it's a pain having
to do everything for Bundler before requiring `pathname` which is a core
Ruby class.

Homebrew's actually ended up using a fair few gems. While we want to
avoid Bundler at runtime (and this PR still does that, in fact uses
Bundler even less at runtime than it did before) writing our own version
to use at build-time seems redundant.