protocol: unify changegroup commands
- add sendchangegroup protocol helpers
- handle commands with None results
- move changegroup commands into wireproto.py
#!/bin/sh
echo "[extensions]" >> $HGRCPATH
echo "hgk=" >> $HGRCPATH
hg init repo
cd repo
echo a > a
hg ci -Am adda
hg debug-cat-file commit 0