Escape ampersand & in the filename also.

I am amazed what stupid filenames some people come up with, instead of
abiding by old good [a-zA-Z0-9] character set and 8.3 filename length...

utils/pdfattach

@@ -13,7 +13,7 @@ progname=$(basename $0)
 function escape_tex_specialchars()
 {
 	local txt=$1
-	local res=$(echo "$txt" | sed -e "s%_%\\\_%g")
+	local res=$(echo "$txt" | sed -e "s%_%\\\_%g" -e "s%&%\\\&%g")
 	echo "$res"
 }