magit-svn-find-rev: bugfix

Don't create a section for no good reason whatsoever.
Also cleanup the other crap this function consisted of.
magit-stgit-show: just wrap around magit-show-commit
magit-stgit-wash-patch: use magit-insert
magit-stgit-wash-patch: fix use of magit-bind-match-strings
magit-stgit-wash-patch: make sure line matches
magit-insert-topgit-topic: fix use of magit-cmd-insert-section

This fixes c2c900aff8508f6882aa06e974c6d5413286abac.
magit-topgit.el: split into sections, rearrange

Split `magit-topgit.el' into the same sections (conceptually) in the
same order as in `magit-stgit.el'.

The new "Commands" section actually does not contain a single command,
but most of these functions should be commands.  Currently they only
hook into existing "action" commands, it would make sense to be able
to invoke them directly.

(Here is another TODO: `magit-topgit-wash-topic' has to be more like
other washers.  Someone who actually uses topgit should do that.)

The main reason the code in the "Mode" and "Topics Section" have
switched positions is because upcoming changes would otherwise cause
the byte-compiler to complain.
magit-insert-topgit-topics: make sure magit-topgit-mode is on
magit-define-section-jumper: absorb magit-goto-section-at-path

Merge `magit-goto-section-at-path' into its only caller
`magit-define-section-jumper'.  This fixes a bug as the former did
not return nil when the section could not be found, but the latter
expected it to do so.  Instead of just fixing that, merge because
the name `magit-goto-section-at-path' is to generic for a function
which only knows about sections that are direct children of the
root section.
magit-status-show-sequence-help: remove option
magit-insert-cherry-help-lines: don't abuse magit-insert-line-section
magit-insert-status-tags-line: use only colors, not verbs

Avoid uncertainty about whether the tag or the branch is the subject
when displaying the current and next tags in the header of the status
buffer, by using just colors to indicate which side has the additional
commits. Previously we used the verbs "ahead" and "behind", and which
one had to be used depended on whether the branch or the tag was
considered the subject of the "sentence".