the verify app man page didn't describe the usage of attime option
even though it was listed as a valid option in the -help message.
This patch fixes this omission.
[B<-untrusted file>]
[B<-help>]
[B<-issuer_checks>]
+[B<-attime timestamp>]
[B<-verbose>]
[B<->]
[certificates]
does not itself imply that anything is wrong: during the normal
verify process several rejections may take place.
+=item B<-attime timestamp>
+
+Perform validation checks using time specified by B<timestamp> and not
+current system time. B<timestamp> is the number of seconds since
+01.01.1970 (UNIX time).
+
=item B<-policy arg>
Enable policy processing and add B<arg> to the user-initial-policy-set