Fix a issue to add duplicate entries into file list
vim-cocoa can be launched from (at least) two different
places: command line (Vim -g) or Finder/Dock.
We're expected to open files dropped on to vim-cocoa's
icon, so we implemented application:openFiles: in our
app controller, however, I didn't expected that method
can also be called when vim-cocoa is launched from
command line, thus will cause the same entry be added
into file list twice (one by vim command line handling
itself, another by application:openFiles:).
So, this patch basically checks if the same entry exists
in the "to-open" list (global_alist) before add it on
to that list at application:openFiles:. In this way,
we can safely avoid duplicate entries.
This bug is triggered by the '-d' option. (Issue 23)