changegroup: factor changelogdone into an argument
The variable was basically tracking whether the current operation
is being performed against the changelog or something else. So
let's just pass such a flag to everything that needs to access it.
I'm still not a huge fan of building changelog awareness into
low-level functions like revision delta generation. But passing
an argument is strictly better than state on the packer instance.
Differential Revision: https://phab.mercurial-scm.org/D4137
changegroup: record changelogdone after fully consuming its data
Setting this as a side-effect of calling _close() is wonky. There's
only one group for changelog data. So we can wait until after all
data has been emitted before recording it.
Differential Revision: https://phab.mercurial-scm.org/D4136