Please refer to this thread and discussion. It is my understanding that this feature (may) be re-introduced in the upcoming version.
I personally do not like the trust idea as too many users rather than thinking if the file actually could have been infected somehow would just trust it. However that said it is being considered for a later upgrade of the 13.0 version.
I would at least run the file at www.virustotal.com to see what the other scanners think.
If you want the file cleared you follow
reply to the email reply you get changing the subject to False+ve and name of detection and say why you think it is ok and where the file comes from. If safe the file should be cleared in 4-5 days if not post back here with rthe analysis id that email has and I will get a tech to fix it.