extensions: add notloaded method to return extensions failed to load Before this patch, there is no easy way to detect if there are extensions failed to load. While this is okay for most situations, chgserver is designed to preload all extensions specified in config and does need the information. This patch adds extensions.notloaded() to return names of extensions failed to load.

histedit: renaming parts to which _histedit was split I recently broke _histedit into multiple functions, each of which had 'action' in its name. This is a little bit confusing since 'action' is the word for an individual histedit plan item (such as edit or pick). To avoid this confusion, these functions are now renamed to contain 'histedit' as part of their names.

histedit: break _histedit into smaller pieces (add _finishaction) This is a part of a bigger effort to refactor histedit with ultimate goal of understanding it.