linkedlist:added comments for list_merge
linkedlist:added list mergesort algorithm description from Simon Tatham's
linkedlist:modified list_merge comments
linkedlist:added list_mergesort function
linkedlist:modified the Makefile and commented old doubly linked list implementation
linkedlist:define prefetch for nothing
linkedlist:when 0 merges are executed,not one merge,a pass of merging along the list is finished.
linkedlist:added listmain.c