[mod_uploadprogress] use splay_tree for req list
[mod_uploadprogress] use splay_tree for req list

(avoids persistent memory allocation for list struct)
(reduce possibility of long-term memory fragmentation due to
mod_uploadprogress)

lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4