Description:
------------
<?php
echo  image_type_to_extension (4)."<br>"; // swf
echo  image_type_to_extension (13)."<br>"; // swf // should be '.swc' 


//if $_FILES['Filedata'] is a swf file and you ....

list(,,$image_type) = getimagesize($_FILES['Filedata']["tmp_name"]);


// then ....

echo $image_type;// 13 // should be '4'

I tried this with a variety of swf files, compiled using CS4, CS3, for AS2 and 
AS3, for FP10 and FP8 but the results are the same regardless (did not try AS3 
for FP8)

Test script:
---------------
<?php
echo  image_type_to_extension (4)."<br>"; // swf
echo  image_type_to_extension (13)."<br>"; // swf

// if $_FILES['Filedata'] is a swf file and you ....

//list(,,$image_type) = getimagesize($_FILES['Filedata']["tmp_name"]);


// then ....

//echo $image_type;// 13

Expected result:
----------------
<?php
echo  image_type_to_extension (4)."<br>"; // swf
echo  image_type_to_extension (13)."<br>"; // swc

Actual result:
--------------
<?php
echo  image_type_to_extension (4)."<br>"; // swf
echo  image_type_to_extension (13)."<br>"; // swf