Apple reset this on every OS X major (and some minor) updates and it
always proves a painful and unnecessary step. Instead just check the
directories we actually care about are writable.

This may mean if these directories do not already exist (although they
are now created by the installed) that `brew link` will fail and require
manual intervention but this seems to be superior for both new and the
majority of existing users.

Also, flag those that we never want to be in a manpage.

Fixed minor typo -- missing preposition.

This document lists Tigerbrew and Linuxbrew as interesting forks, not
branches (they used to be "Interesting Branches (aka forks)" but that
changed in b7455469), so "Interesting Taps & Branches" is a more fitting
title.

The term "branches" is also presumably confusing to folks with a shallow
understanding of GitHub and/or git who may not realize how GitHub forks
and git branches are related.

Add --full-name option to brew deps command,
which displays the full name of dependencies.

`--HEAD` defaults to `:branch => "master"` so document that.

Closes #722.

Forgot this in #731.

This option does more than just print warnings so let's make a more
generic description with a more specific example.

Closes #716.

- Inconsistent or unneeded indentation
- Missing or superfluous empty lines
- Missing or wrongly formatted arguments in command summary
- Missing punctuation

And arguments can be passed through to it.

Tweak produced out of conversation in
https://github.com/Homebrew/brew-evolution/pull/8.

Add a `brew update --force` to side-step all of the clever optimisations
we have to detect if an update is unnecessary. That means if those
optimisations go wrong in future we can tell people just to run this
single command.

This would have been a useful workaround for the issue fixed in 985c672b.

Roll this out to everyone (not just developers) and document the
environment variables used for configuration.