VC / Git: amend function / mark for add / timing

[David Reitter]

It would be nice if VC provided a function to add the "--amend"  
argument to "git commit" so that the last commit is amended.  This is  
useful when one forgets to check in file, especially after using C-x v  
v to commit a single file.   The logical binding I thought of at first  
was C-u C-x v v, but that seems to do something else.

Also, it's not obvious at all from the menu how to mark the file in  
the current buffer for addition, i.e. do a "git add".  Is this  
possible at all?

Finally, it takes several seconds when I open a file that's under git  
version control.  What can we do about this?  I think I complained  
about it at some point, and we didn't find a solution.   I'd rather  
have VC functions blocked until the file status is obtained  
(asynchronically) rather than having to wait before I can do any  
viewing/editing on the file.  (But this particular solution would  
require a number of changes.)

Many thanks for improving vc-git!