manual: Add a section on rebuild of the "next" branch.

diff --git a/web/manual.m4 b/web/manual.m4
index 14feb5739c771bd2ee16e516b0d36d389d1b454f..946b9d0953621b23a3a6e30e62c211674d0c6ea5 100644 (file)
--- a/web/manual.m4
+++ b/web/manual.m4
@@ -1866,6 +1866,11 @@ have been merged into "next" are usually not rebased, and you can find
 the tip of topic branches you are interested in from the output of
 "git log next"). You should be able to safely build on top of them.
 
+However, at times "next" will be rebuilt from the tip of "master" to
+get rid of merge commits that will never be in "master. The commit
+that replaces "next" will usually have the identical tree, but it
+will have different ancestry from the tip of "master".
+
 The "pu" (proposed updates) branch bundles the remainder of the
 topic branches.  The "pu" branch, and topic branches that are only in
 "pu", are subject to rebasing in general.  By the above definition