bug#11096: 24.0.94; vc-ediff: Minor improvements

[Jambunathan K]

Thanks a lot for vc-ediff.  It is quite useful.

Some suggestions: 

1. Emulate vc-diff and report a helpful message if the file in question
   has no changes.

,---- *Messages*
|      No changes between working revision and workfile
`----

2. The following message is confusing and the y-or-n prompt is a minor
   annoyance.

,---- *Messages*
|      File org-e-odt.el.~master~ changed on disk.  Reread from disk? (y or n)  
y
`----


Attachments
===========

,---- Behaviour of vc-diff when file is unmodified
| Finding changes in c:/Documents and Settings/kjambunathan/My Documents/My 
Data/src/org-mode/EXPERIMENTAL/org-e-odt.el...
| Running git diff-index --exit-code -p HEAD  -- org-e-odt.el in foreground...
| Running git diff-index --exit-code -p HEAD  -- org-e-odt.el...OK = 0
| No changes between working revision and workfile
`----

,---- Behaviour of vc-ediff when file is unmodified
| Finding changes in c:/Documents and Settings/kjambunathan/My Documents/My 
Data/src/org-mode/EXPERIMENTAL/org-e-odt.el...
| Checking out c:/Documents and Settings/kjambunathan/My Documents/My 
Data/src/org-mode/EXPERIMENTAL/org-e-odt.el.~master~...
| Running git cat-file blob HE... ....OK = 0
| Checking out c:/Documents and Settings/kjambunathan/My Documents/My 
Data/src/org-mode/EXPERIMENTAL/org-e-odt.el.~master~...done
| File org-e-odt.el.~master~ changed on disk.  Reread from disk? (y or n)  y
| Computing differences between org-e-odt.el.~master~ and org-e-odt.el ...
| Processing difference regions ... done
| Quit this Ediff session? (y or n)  y
`----