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
merge SPC-for-args tarsius/pr/squash