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

adding bar
adding foo
% state dump
a   0         -1 baz
n 644          0 foo
r   0          0 bar
% status
A baz
R bar
C foo
% state dump
n 666         -1 bar
n 666         -1 foo
% status
! bar
? baz
C foo