magit-revision-refresh-buffer: Avoid file refname

When both a file and revision have the same name, 'git show' fails:

    fatal: ambiguous argument 'foo': both revision and filename
    Use '--' to separate paths from revisions, like this:
    'git <command> [<revision>...] -- [<file>...]'

As a result, `magit-revision-refresh-buffer' showed an empty buffer.

Use '--' to specify that this argument is a revision.
run section movement hook when using line-wise fallback

Rename `magit-goto-section-hook' to `magit-section-movement-hook'.
Rename `magit-goto-section' to `magit-section-goto', and instead of a
section also accept a number as argument.  If it's a number then it
always is either 1 or -1, move by that many lines in that direction,
using `forward-line'.

The movement commands which call `magit-section-goto' previously only
called it (under its old name) when an appropriate section existed in
the desired direction.  When that was not the case, then they just used
`forward-line' directly, which prevented the movement hook from running.
magit-section-goto-successor: more explicit root section check
magit-section-goto-successor: only use magit-goto-char once

When returning to the start of the successor section after detecting
that moving by the line offset would move us out of the successor,
just use `goto-char'.
Merge pull request #1558 from kyleam/n/fix-rev-ambig

magit-revision-refresh-buffer: Avoid file refname
magit-log-oneline-re: fix for orphaned branches

Fixes #1556.
Merge branch 'master' into next

Conflicts:
	magit.el

Which was resolved by moving the change to magit-log.el
where the respective code lives now.
magit-diff-dwim: bugfix
Check for existance of the directory in wip.

If a buffer edit a file in an non existing directory
magit-inside-worktree-p fill fail with an error. As
turn-on-magit-wip-save is meant to be in post-command-hook, it must not
fail with an error, so we check if the directory exists.
Merge pull request #1564 from vanicat/t/turn-on-should-no-fail

Check for existance of the directory in wip.
magit-read-file-trace: bugfix
magit-diff-select-algorithm: move definition
magit-diff-auto-show-p: move definition
magit-diff-toggle-refine-hunk: move definition
magit-{visit-file,hunk-file-position}: move definitions
rename magit-visit-file to magit-diff-visit-file
rename magit-hunk-file-position to magit-diff-file-position