[Clamav-devel] PNG scanning code change

[Aldo Mazzeo]

Hello,
I changed the current implementation of the PNG scanner (which was mostly a
PNG validator) into an exploit seeker with PR #73. I added the detection
for a couple of exploits I knew (but this thing can be totally expanded); I
actually don't know if I used correctly the cli_append_virus function as I
made up the names of the heuristics by pointing out which CVE is associated
to the detected vulnerability, but hopefully I did this right.

Also, now it scans the overlay (if present).