Just wanted the OP to know it still might be a false positive, I all ready emailed support and are waiting to hear back from them. I do know for a fact the file is for some type of CD copy protection, it rights the file to the temp directory to check that a authentic CD is being used, cause thats what Blizzard told me when I spoke with them about Warcaft 3 and World of Warcraft. From all my research on-line, the OP’s issue might be related to my issue and might be pulling his hair out for nothing if it is a false positive.
Let us know what you come up with max, cause I would really like to get this solved 
Also I reanylized the file and it came up with less detections…only 2 less but still 
http://www.virustotal.com/analisis/7f1553c2ced0f7a7f7980e729c9cbfbe
AND I tested a game called Vietcong that is made by the same game makers and it also created a sinfnt.dll in the temp folder, but this was not detected as a virus by avast…o.O
Heres the Virus total for that sinfnt.dll file
http://www.virustotal.com/analisis/01447eb60bcc0a8d678a9393fab7a367esults
Yes let us know what they say!
I have the same problem. I just shut down and Avast to play Mafia. I have a lot of other virus protection and trojan protection and none of them detects it as a problem. Avast should have some way to let you allow all the program to run.