remove unused variable
previous-sibling falls back to previous section

This makes `magit-goto-previous-sibling-section' symmetric with
`magit-goto-next-sibling-section'.

It was falling back to parent instead, which meant that
`magit-goto-previous-sibling-section' got "stuck" in the lines between
sections (they belong to top status section so there is no parent or
siblings).
soft require magit-log-edit

The old commit mode is now available as a separate package.  To make it
easier for its users soft require it.  If they have it installed it will
be loaded, causing some things defined in `magit.el' to be overridden.
If someone has it installed but doesn't want it to be loaded then he
should make up his mind.
magit-anything-staged-p: use git-diff-files
add new predicate magit-anything-unstaged-p
magit-stage-all: without a partial index don't require confirmation
magit-unstage-all: without a partial index don't require confirmation
magit-wash-diffs: fix recent bug

Recent changes to how diffs are washed introduced a bug that resulted in
the first file section starting on the first line before it.  This fixes
it in not so great way.  That is okay because the respective code area
will soon be further cleaned up anyway.
magit-display-process: don't show progress if process has terminated

Close #996.
Merge branch 'pr/fix-display-process'
magit-unstage-all: require confirmation with untracked files
Merge pull request #1001 from npostavs/goto-sibling

`magit-goto-previous-sibling-section` gets "stuck" between sections
magit-ignore-item: ask to untrack file before ignoring

Close #370.
magit-read-file-from-rev: allow selecting a tree

Teach `magit-read-file-from-rev' to offer
trees, not only blobs, for completion.
magit-diff-with-mark: only one argument RANGE

Replace `magit-diff-with-mark's MARKED and COMMIT arguments with just
RANGE, making it consistent with other diff commands.  Keeping these
arguments for non-interactive use would not make sense since the marked
commit is determined inside `interactive'.  Except for that part it
behaves the same ad `magit-diff', the latter should therefor be used
non-interactively.
git-am action --- apply mbox from within magit

This patch defines the git-am action and the `magit-apply-mailbox'
function and binds them to "j".

The existing interactive rebase machinery is extended to handle "git am"
mailbox applications.  Git shares structure between "git rebase" and
"git am", (e.g., they both use the .git/rebase-apply directory) so this
is a natural extension.
Merge branch 'pr/git-am'
magit-diff: fix regression

Since 4bb6cb07b9dab950742f3edd7cfa38afe1721839 `magit-diff', when the
diff buffer already existed, did not use the current `default-directory'
but that of the buffer.  Now it resets the local value again.
delimit sections with markers

Store markers instead of positions in the BEGINNING and END slots of
section structs.  This makes it possible change text before a section
after it has been washed.  Once case in which this is useful is when
washing a section properly requires information that isn't available
until another section that textually comes later has been washed.

The BEGINNING marker is initially set to not advance when text is
inserted at the place it points to (or nothing would ever become part
of the section), but once washing is done it is changed to advance.
optionally append the number of children to section headings

Close #548.