Trust but verify 'scutil' to return ComputerName

Apparently, it is possible to set up a Mac such that
`scutil --get ComputerName` hasn't been set.

This change checks if that fails and falls back to the original
mechanism.

Closes #2155
Closes #2183
fix missing add-zsh-hook in pygmalion.zsh-theme

Fix "command not found: add-zsh-hook" since #3053 removes `autoload -U add-zsh-hook`
Symfony2 plugin use first console found
Symfony2 plugin look for files only
Symfony2 plugin autocomplete for app/console and bin/console
Merge pull request #3087 from hacfi/symfony

Symfony2 plugin use first console found
Merge pull request #2743 from docwhat/issue-2155-scutil

Trust but verify 'scutil' to return ComputerName
Merge pull request #3072 from clippit/patch-1

Fix missing add-zsh-hook in pygmalion.zsh-theme
Revert "Exit early from git plugin if not in git repo."
Merge pull request #3095 from robbyrussell/revert-1504-master

Revert "Exit early from git plugin if not in git repo." due to #3082
AWS plugin: add MFA device handling

Added a couple of commands for MFA device handling using oathtool.
- aws_mfa_add_device: adds a virtual device, encrypting the secret seed
  using gpg and storing it in $AWS_HOME/account_name.mfa.asc.
  It also auto-completes profile names, so the account is associated to an
  existing profile.
- mfa: generates an MFA code based on the encrypted secret seed. It requires
  oathtool to be installed, and optionally integrates with the clipboard
  using pbcopy (on Mac OS X) and xsel (on X11 systems)
added an alias for changing the AWS access key set on a profile
style cleanups