Gnus: Improve subthread sorting;

 make subthread sorting customizable and add docs for it

* doc/misc/gnus.texi (Sorting the Summary Buffer): Document new defcustom
`gnus-subthread-sort-functions' and remove the obsolete documentation
of `gnus-sort-threads-recursively'.

* lisp/gnus/gnus-sum.el (gnus-subthread-sort-functions): New defcustom.
(gnus-sort-threads-recursively): Delete defcustom.
(gnus-sort-threads-recursive): Adapt accordingly.

* lisp/gnus/gnus-sum.el (gnus-sort-subthreads-recursive): New function.
(gnus-sort-threads-recursive): Use it.
(gnus-sort-threads): Unconditionally call `gnus-sort-threads-recursive'
again.  Now that determines how to sort subthreads.

2 files changed, 14 insertions, 5 deletions

diff --git a/doc/misc/ChangeLog b/doc/misc/ChangeLog
index b306ce5ba0a..9b45ac06f4c 100644
--- a/doc/misc/ChangeLog
+++ b/doc/misc/ChangeLog
@@ -1,4 +1,10 @@
-2013-07-29  David Engster <deng@randomsample.de>
+2013-07-30  Tassilo Horn  <tsdh@gnu.org>
+
+        * gnus.texi (Sorting the Summary Buffer): Document new defcustom
+        `gnus-subthread-sort-functions' and remove the obsolete documentation
+        of `gnus-sort-threads-recursively'.
+
+2013-07-29  David Engster  <deng@randomsample.de>
 
         * eieio.texi (top): Make clear that EIEIO is not a full CLOS
         implementation.
diff --git a/doc/misc/gnus.texi b/doc/misc/gnus.texi
index 5f9e0b9db28..808bd2b114b 100644
--- a/doc/misc/gnus.texi
+++ b/doc/misc/gnus.texi
@@ -7394,10 +7394,13 @@ say something like:
         gnus-thread-sort-by-score))
 @end lisp
 
-By default, threads are sorted recursively, that is, first the roots,
-then all subthreads, and so on.  If you feel more like sorting only
-the roots, so that inside a thread the original chronological order is
-retained, you can set @code{gnus-sort-threads-recursively} to nil.
+By default, threads including their subthreads are sorted according to
+the value of @code{gnus-thread-sort-functions}.  By customizing
+@code{gnus-subthread-sort-functions} you can define a custom sorting
+order for subthreads.  This allows for example to sort threads from
+high score to low score in the summary buffer, but to have subthreads
+still sorted chronologically from old to new without taking their
+score into account.
 
 @vindex gnus-thread-score-function
 The function in the @code{gnus-thread-score-function} variable (default