pager: ensure wrapped dispatch._runcommand runs before color's An upcoming patch will teach color to potentially act differently if the pager is active. Since both extensions wrap the same function (dispatch._runcommand) to change behavior, we must guarantee that pager's wrapped function runs before color's so color may read the breadcrumb left by pager.

pager: set an attribute on ui indicating that a pager is active A subsequent patch will teach the color extension to do different things depending on whether a pager is active. This patch leaves a breadcrumb on the ui instance to allow it do that that.

extensions: support callbacks after another extension loads An upcoming patch will introduce a dependency between the color and pager extensions. To prepare for this, we teach extensions how to register callbacks that can execute when another extension loads. This patch is based on code provided by Matt Mackall. But significant parts have changed (such as the ability to register multiple callbacks and the change in behavior to always call a callback). I believe that always firing the callback is a good practice. I think the common use for this feature will be for extensions to say "run this one-time setup code, after this other extension if possible." Always running the callback will facilitate this.