tests/test-commit-copy.out

changegroup: avoid large copies

- handle chunk headers separately rather than prepending them to
  (potentially large) chunks
- break large chunks into 1M pieces for compression
- don't prepend file metadata onto (potentially large) file data

foo renamed from bar:26d3ca0dfd18e44d796b564e38dd173c9668d3a9
   rev    offset  length   base linkrev nodeid       p1           p2
     0         0       6      0       0 26d3ca0dfd18 000000000000 000000000000
     1         6       7      1       1 d267bddd54f7 26d3ca0dfd18 000000000000