When the "attention dialog" is given (E325), there is a list of 
options for the
user. For example, if I am editing "a.c" in one terminal session, and try to
open it in another one, vim finds that there is already a swap file 
for a.c and
gives me the following warning:

     E325: ATTENTION
     Found a swap file by the name "a.c_swp"
                 dated: Fri Dec 17 20:45:22 2010
             [cannot be opened]
     While opening file "a.c"
                 dated: Fri Dec 17 20:45:28 2010
         NEWER than swap file!

     ...

     Swap file "a.c_swp" already exists!
     [O]pen Read-Only, (E)dit anyway, (R)ecover, (D)elete it, (Q)uit, (A)bort:

I believe that the option to "(D)elete" the swap file should only be displayed
if the "other" process is not running, i.e. if it has crashed.

I did not find any documentation for this, but
- this makes sense,
- this seems to be the intention in memline.c, findswapname(), see the use of
   variable process_still_running

Currently, the option to Delete the swap file is displayed even when the other
process is still running. It probably isn't very "healthy" to delete the swap
file then.