Exclude web pages from media library import

When I run a media library import on my site, it grabs not only images and audio and video files (which I want) but webpages (HTML, PHP, etc.) which I don’t want, as it wastes space on my drive and in my DB. How can I prevent it from importing webpages/HTML & PHP file types?

http://wordpress.org/extend/plugins/w3-total-cache/