[SECURITY] Corrected advisory on wu-ftpd-academ buffer overflow

The previous advisory concerning wu-ftpd-academ contained an error: the md5sum given for wu-ftpd-academ2.4.2.16-12.2i386.deb was incorrect. The correct md5sum is b851adb345917a6f92e8b03f8cc97ff2. I apologize for the confusion this has caused. The complete, updated, text of the advisory follows...