This is a mirror of http://www.vim.org/scripts/script.php?script_id=4291

Automatically adds a global mark whenever you leave Insert mode, so you can
easily return to text you were last working on, even if you have moved to a
different buffer!  I tend to need this after I have been navigating around
files to do some research.  This saves us from hitting Ctrl-O repeatedly!

It sets global marker Z so you can jump back with g'Z but this is also bound to
the C-Y key for convenience.

ISSUES: not all edits require Insert mode.  e.g. undo or 4r0
And leaving Insert mode is not always an edit (e.g. Insert mode on a
conqueterm, or i<Esc> aborted edit).

