scmutil: split platform-specific bits into their own modules This parallels what's done for the util module, which imports either mercurial.posix or mercurial.windows as 'platform' and then slurps the appropriate functions into its own namespace.

backout: call cmdutil.commit directly instead of commands.commit This cleans up the messiness of having one command call another, and makes the backout command robust against changes to the commit command.

commit: factor out status printing into a helper function We create a new function commitstatus() in cmdutil that handles printing the status message(s) after a commit. This will allow other commit-like commands to use it, and in particular is step 2 towards removing backout's call to commands.commit.

backout: remove unnecessary dict copy This is step 1 to remove backout's call to commands.commit. We don't use the options again anywhere below except for backout's own purposes, specifically choosing a merge tool, so we just write the commit options in directly.