Check for diff3 is incorrect in ediff-exec-process

[Roman Belenov]

ediff-exec-process checks whether it uses diff3 (in order to discard
--binary flag which diff3 doesn't support) using (string-match
"buffers3" job-name) It fails when ediff is used by PCL-CVS and
--binary option is passed to diff3 which results in an error (I'm
using Windows 2000 so that system-type is windows-nt).

IMHO (string-match "diff3" program) check is more correct (reaction to
'--binary' option is the property of diff3 utility itself).

-- 
                                                        With regards, Roman.