Lumaraf on "[Plugin: W3 Total Cache] Caching should not depend on exact case of Content-Type"

According to RFC 2616 ("Hypertext Transfer Protocol -- HTTP/1.1", 4.2 Message Headers) HTTP header field names are case-insensitive.
To match the RFC and improve compatibility the check for the "Content-Type" header in W3_PgCache#_is_cacheable_content_type() should be done with stripos instead of strpos.

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