"Acting>Visit": absorb related "Acting" subsections
magit-show: move definition
magit-dired-jump: move definition
magit-dired-jump: define on load

Define `magit-dired-jump' when loading `magit.el' instead of delaying
that until after `dired-x' is loaded.  This allows autoloading this
command and because we are soon going to use `dired-jump' elsewhere
too, we gain nothing from not defining this command instantly.
magit-dired-jump: fix doc-string
magit-dired-jump: cosmetics
magit-visit-file-item: demote to non-interactive function

Demote `magit-visit-file-item' from a command to a non-interactive
function.  There was no key binding for this command and users should
just use `magit-visit-item' instead.  Until some commits ago this
function had to be a command because the latter called it using
`call-interactively', but that has been fixed now.
magit-visit-file-item: prevent future bug

As of now this is a cosmetic and semantic cleanup, but future changes
will actually make this necessary.
magit-visit-file-item: visit directory using dired-jump
magit-read-stash: new function

This function could be nicer, but I don't actually expect it to be used
very often, so I won't do it until my todo list has shrunk.  It is
needed because `magit-show-stash' has to be turned into a command and
for that some input reader is needed.
magit-show-stash: promote to command

It doesn't make any sense for this to be a non-interactive function when
the related `magit-show-commit' is a command.
magit-wash-log: use button for "show more history"
magit-visit-item: remove `branch' section case

The meaning of "visit" is very different for all other cases handled by
`magit-visit-item'.  Because there are several other methods for showing
more history, we don't need to keep this one.
magit-checkout-branch-at-point: new command

Add the new command `magit-checkout-branch-at-point' and bind RET to it
in `magit-branch-manager-mode'.

Previously `magit-visit-item' did checkout the current branch when
invoked on a `branch' section, but that is wrong and this commit also
drops that case.  Using the buffer local keymap is the right thing to do
here - we should not abuse the `magit-section-action' functionality.  If
we always did what we were previously doing here, then section actions
would just become another way of implementing local keymaps (whether
that be buffer local keymaps or the `keymap' text property), and a
rather poor one at that.

Only actions that are fairly close to one another should ever be grouped
in a `magit-section-action' or `magit-section-case'.  This isn't the
case here.  Bringing up some information in some buffer about the thing
at point in the current buffer, as done in the other cases, is *very*
different from checking out a branch.
magit-show-item-or-scroll-{up,down}: cosmetics
magit-show-item-or-scroll-{up,down}: move definitions

These commands are not related to `magit-show' and the other commands
in "Acting>Visiting", they are related to `magit-show-commit' (and
`magit-show-stash').
magit-show-item-or-scroll: new function

Add new function `magit-show-item-or-scroll' to decide on behalf of the
commands `magit-show-item-or-scroll-{up,down}' whether the commit buffer
should be scrolled and do it if appropriate.  Previously that was done
in `magit-show-{commit,stash}', which lead to these commands having an
interface that leaked implementation details.

Now that `magit-show-{commit,stash}' are not overloaded anymore, replace
their SELECT argument with NOSELECT, and remove the SCROLL argument.
Also change the argument order.

Remove most of `magit-show-commit's doc-string, some of that will come
back later.
magit-show-item-or-scroll: prompt for commit as fallback

Previously when `magit-show-item-or-scroll-{up or down}' was invoked but
point wasn't on a commit or stash, that caused the current buffer to be
scrolled.  But that didn't really make any sense, so now we instead
prompt for a commit to visit.
magit-show-item-or-scroll: wrap around to opposing buffer boundary
magit-show-{commit,stash}: use magit-mode-display-buffer