Merge branch 'rs/more-buffered-io'

Use more buffered I/O where we used to call many small write(2)s.

* rs/more-buffered-io:
  upload-pack: use buffered I/O to talk to rev-list
  midx: use buffered I/O to talk to pack-objects
  connected: use buffered I/O to talk to rev-list

diff --cc connected.c
Simple merge

diff --cc midx.c
Simple merge

diff --cc upload-pack.c
Simple merge