Add an argument sigil in a Bookmark class method
Add an argument sigil in a Bookmark class method

A missing argument sigil is effectively a syntax error in VimL. The
function in which the error occurred was called in the execution of at
least three buffer-local NERDTree commands:

 1. :Bookmark (specifically, when trying to overwrite a Bookmark)
 2. :OpenBookmark
 3. :RevealBookmark

Only one specific type of error message associated with these commands
is fixed here (see issue #677).

The problems with the above commands are not fully addressed by this
commit, and their behavior can be improved immensely by further
refactoring. However, no one has been able to even use these commands at
all before now because the fix given here was not in place.

More work will need to be done to improve the behavior of these commands
so that they truly function as any reasonable user would expect.

Fixes #677.

tschundler/dotfiles,tschundler/dotfiles,tschundler/dotfiles