Eshell fringe status indicators

Show an indicator of the status of the last command run in eshell. To use, enable eshell-fringe-status-mode in eshell-mode. The easiest way to do this is by adding a hook:

(add-hook 'eshell-mode-hook 'eshell-fringe-status-mode)

This mode was inspired by the status indicators of Final Term.

Some extra fringe bitmaps are provided. In case you prefer either or both of them over the default arrow bitmap. These are efs-plus-bitmap and efs-minus-bitmap. These show a + and - in the fringe respectively, instead of an arrow. These can be used by setting the eshell-fringe-status-success-bitmap and the eshell-fringe-status-failure-bitmap options.

Note: This mode uses a rather hackish way to try and keep everything working in regard to eshell-prompt-regexp, so if anything breaks please let me know.