On save, only unset 'modified' for the current filename

If the buffer is being saved to a different filename, then this buffer
should still be modified as its backing file is still different than the
buffer.

Signed-off-by: James McCoy <jamessan@jamessan.com>

plugin/gnupg.vim

@@ -761,7 +761,9 @@ function s:GPGEncrypt()
   endif
 
   if auType == 'BufWrite'
+    if expand('%:p') == filename
       setl nomodified
+    endif
     setl buftype=acwrite
     let &readonly = filereadable(filename) && filewritable(filename) == 0
   endif