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
Use $OSTYPE instead of uname to speed things up

The $OSTYPE variable is set at ZSH compile time and can be safely used
to determine the OS of the system. e.g. darwin (os x)
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
Support dynamically defined Vagrant machines
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
Merge pull request #2744 from docwhat/ostype-not-uname

Use $OSTYPE instead of uname to speed things up
Merge pull request #2811 from stucki/multiple-vagrant-machines

Support dynamically defined Vagrant machines
Changed upgrade remote to 'upstream'
Show literal command in title instead of unaliased
Added doubleend theme from Nettuts+

This commits have been squashed:
- Added doubleend theme from Nettuts+
- Better git prompt on doubleend theme
- Syntax fixes, precmd inside $PROMPT to work with Ctrl+L
- Refactoring doubleend theme
- Cleanup, comments added
- Variables wrapped in double quotes in spacing()
- Modified $PROMPT to single line; cleanup.
- Modified CTRL+L behaviour to execute precmd() prompt line
- Renaming functions. Fixes git autocompletion
- Theme refactor. Works on CTRL+L and resizing
- Simplification of if-else
Brings all directory stuff to directories.zsh

- Cleans out aliases.zsh.
- Removes unneeded cd function.
Pushes autoenv code to its plugin.

Sources the activate.sh file or informs the user, that its not
available.
Overriding the cd function, as it was formerly done, is not needed
anymore, activate.sh does this by itself.
Refactors history alias and moves it.

More compact case statement instead of the ugly if elif... else
statement. Moves it to history.zsh