add mergesort() for linked lists

This adds a generic bottom-up mergesort implementation for singly linked
lists.  It was inspired by Simon Tatham's webpage on the topic[1], but
not so much by his implementation -- for no good reason, really, just a
case of NIH.

[1] http://www.chiark.greenend.org.uk/~sgtatham/algorithms/listsort.html

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
index 3b7680e..1787c81 100644
--- a/.gitignore
+++ b/.gitignore
@@ -180,6 +180,7 @@
 /test-index-version
 /test-line-buffer
 /test-match-trees
+/test-mergesort
 /test-mktemp
 /test-obj-pool
 /test-parse-options