Merge branch 'jv/use-larger-buffer-in-upload-pack'

"git upload-pack" (the other side of "git fetch") used a 8kB buffer
but most of its payload came on 64kB "packets".  The buffer size
has been enlarged so that such a packet fits.

* jv/use-larger-buffer-in-upload-pack:
  upload-pack.c: increase output buffer size