Add cabal_sandbox_info function

Reports whether the current working directory is within a
sandbox. Useful to check before installing Cabal packages into the
global registry.
Merge pull request #2541 from puffnfresh/cabal-sandboxes-info

Add cabal_sandbox_info function
Adieu l'ami.

 @jimweirich -- You will be missed.
Avoid evaluating special chars in $LINE on title command (fixes #2234)
Added doubleend theme from Nettuts+
Better git prompt on doubleend theme
Syntax fixes, precmd inside $PROMPT to work with Ctrl+L
Use single quotes also in $LINE definiton
Revert previous commit, escape %
Refactoring doubleend theme
Cleanup, comments added
Fixed CORRECTION flag in .zshrc
Changed correct_all option to correct

'correct_all' looks for errors in commands and arguments
'correct' only looks for errors in commands
Avoid 'title:parse error' with single quotes in $CMD
Fixes #2182
Fixed output of user prompt colors
Revert "Fixed output of user prompt colors"

This reverts commit ac62724da5a9ad91b80618338f8413516e29a500.
Messed up command completion.
Variables wrapped in double quotes in spacing()

Vars that can contain spaces or other special characters mess up the syntax.
Modified $PROMPT to single line; cleanup.

With multiline PROMPT weird things happen, for example when resizing.
Modified CTRL+L behaviour to execute precmd() prompt line
Renaming functions. Fixes git autocompletion