Bug#941329: /usr/bin/grep-excuses: grep-excuses: Mention --autopkgtests switch as well in usage output

[Salvatore Bonaccorso]

Package: devscripts
Version: 2.19.6
Severity: minor
File: /usr/bin/grep-excuses

Hi

grep-excuses manpage documents the --autopkgtests whilst this is
missing in the usage text from grep-excuses.

Regards,
Salvatore