dispatch: use the repo path found by early parsing This lets us simplify things a bit.

dispatch: parse and apply -R early This allows us to use extensions specified in .hg/hgrc. Unfortunately, this requires us to parse that file twice, but performance impact on the version command appears to be less than 1%.

dispatch: parse and apply cwd opt early

dispatch: rename variables after code motion

dispatch: hoist debugging hook to runcatch

dispatch: move dispatching code to cmdutil

dispatch: move runcommand to cmdutil

dispatch: pull final command execution into its own function

dispatch: reduce nesting by moving parsing exceptions

dispatch: move signal and exception handling to its own function