imagecache 5.x-1.6

Changes since DRUPAL-5--1-5:

• some minor cleanups to .info and .install switched package to ImageCache and module name to ImageCache.
• backported header responses from 2.x.
• added some good watchdogs and more error checking/reporting.
• cleaned up lock/tmp file handling. register_shutdown_function is my friend.
• removed some cruftiness from the processing loop and race handling.
• new tmp filename tmp_imagecache_{md5(src)}_{preset}_{basename(src)}, so they are guaranteed unique and mostly identifiable.
• removed optional use of mime_content_type.
• added 307 Location header for images already being process to cause reload of current page... This should try to reload a few times hopefully giving us enough time to finish processing the image.
• #253145 (a.a.egoroff) Preset names shouldn't be translated via t().