dispatch: always load extensions before running shell aliases (issue5230) Before this patch, we may or may not load extensions for shell aliases depending on whether the command is abbreviated or not. Loading extensions may have useful side effects to shell aliases. For example, the pager extension does not work for shell aliases. This patch removes the code checking shell aliases before loading extensions to give the user a more consistent experience. It may hurt performance for shell aliases a bit without chg but the correctness seems worth it. It will also make the behavior consistent with chg since chg will always load all extensions before running commands.