[Tilecache] Setting Content-type header in S3

[Bruce Rindahl]

I am storing tile in S3 but I need to set the content-type (image/png) 
for access outside of TileCache.  I see the S3.py library has this 
available but I can't seem to set this value in tilecache.cfg.  
Otherwise a direct call to the S3 file gives a mime type 
binary/octet-stream.
Thanks
Bruce