magit-diff-none: inherit from default face

Previously we inherited from `diff-context' but because that does not
set a background color in the default them that meant that unchanged in
diffs were highlighted.  Since we by default use a rather ugly color for
that purpose, that was not acceptable.

See issue #1042.
Revert "magit-diff-none: inherit from default face"

This reverts commit 93a504b6c1ec12ac82612003dd4fcbc4d5aa8cab.
magit-log-long-re: rename from magit-log-longline-re

Logs of type "long" do not consist of one long line per commit, as
opposite to a "short oneline" per entry.  They commit is represented
by *multiple* lines, which usually are *shorter* than those used by
logs of type "oneline".  The name of this variable probably used to
contain "longline" instead of "long" to achieve some misguided
consistency with "oneline"; fix that.
magit-wash-commit: lose whitespace and a comment
magit-wash-commit: simplify propertizing first line
magit-format-ref-labels: new function
magit-wash-log-line: use magit-format-ref-labels

This has to unfortunate but acceptable consequence that when there are
only "uninteresting" refs then, when showing a "long" log the revision
hash is abbreviated just if there were at least one "interesting" ref.
In the latter case we do so to make room for the displaying the refs,
in the former case we don't need to make room, but now do so anyway.
However that doesn't really matter.
magit-wash-commit: use magit-format-ref-labels

... to format the refs at the end of the first line, if any.
rename section "Revisions and Ranges" to just "Revisions"

It also contains things to related references and tags (and files);
a more generic "Revisions" serves better than a overprecise but
incorrect heading.  Also remove the subsection headings.
magit-format-rev-summary: new function

... replacing `magit-format-commit'.

Now the rev on "Head", "Rebasing", and "Applying" header lines
in Magit buffers is colorized like they are in most other places.
Merge branch 'pr/goodies'
magit-insert-empty-line: move definition
magit.el: assimilate magit-bisect.el

Copy existing code as-is, except that it is reordered and most
doc-strings and comments are removed.
magit-bisecting-p: renamed from magit--bisecting-p
magit-bisect-reset: no error if nothing to reset

Running `git bisect reset` when there is no running or finished bisect
does nothing (no error).  That's good enough for use, let's not perform
a needless test and raise an error if it fails.

That will also make it easier later on.  We start to benefit in this
commit already by removing the "reset" special case in
`magit--bisect-cmd'.
magit-{insert-bisect-rest,log-bisect-vis-re}: new fn/var

And teach `magit-wash-log-line' about the new log style
introduced by the above, and add `magit-insert-bisect-rest'
to `magit-status-sections-hook'.
magit-bisect-visualize: remove command

Since we now display the respective information directly in the status
buffer, we no longer need this command.
magit-insert-bisect-log: new function

And new function `magit-insert-bisect-log'
and add it to `magit-status-sections-hook'.
magit-log-head-label-bisect-skip: new face

Add new face `magit-log-head-label-bisect-skip' and
add a matching entry to `magit-refs-namespaces'.
magit-{wash-wash-bisect-log,log-bisect-log-re}: new fn/var

And use the new washer in `magit-insert-bisect-log',
and teach `magit-wash-log-line' about the new log style.