commands: create a "mercurial.cmd_impls" module to host graft The "mercurial.commands" have been overweight for a while. We create a namespace dedicated to host smaller modules containing code revelant to a specific command. This should result in more isolated snd manageable module. We start with moving the code for "hg graft" in "mercurial.cmd_impls.graft" before doing more work on it. Since that code was about 5% of "commands.py" this seems like a success.