Merge branch 'rs/mergesort'

The mergesort implementation used to sort linked list has been optimized. * rs/mergesort: test-mergesort: use repeatable random numbers mergesort: use ranks stack p0071: test performance of llist_mergesort() p0071: measure sorting of already sorted and reversed files test-mergesort: add unriffle_skewed mode test-mergesort: add unriffle mode test-mergesort: add generate subcommand test-mergesort: add test subcommand test-mergesort: add sort subcommand test-mergesort: use strbuf_getline()