hgext: add largefiles extension This code has a number of contributors and a complicated history prior to its introduction that can be seen by visiting: https://developers.kilnhg.com/Repo/Kiln/largefiles/largefiles http://hg.gerg.ca/hg-bfiles and looking at the included copyright notices and contributors list.

Greg Ward, author of the original bfiles extension
Na'Tosha Bard of Unity Technologies
Fog Creek Software
Special thanks to the University of Toronto and the UCOSP program