Merge branch 'nd/rebase-show-current-patch'

The new "--show-current-patch" option gives an end-user facing way
to get the diff being applied when "git rebase" (and "git am")
stops with a conflict.

* nd/rebase-show-current-patch:
  rebase: introduce and use pseudo-ref REBASE_HEAD
  rebase: add --show-current-patch
  am: add --show-current-patch

Documentation/git-rebase.txt

@@ -12,7 +12,7 @@ SYNOPSIS
 	[<upstream> [<branch>]]
 'git rebase' [-i | --interactive] [options] [--exec <cmd>] [--onto <newbase>]
 	--root [<branch>]
-'git rebase' --continue | --skip | --abort | --quit | --edit-todo
+'git rebase' --continue | --skip | --abort | --quit | --edit-todo | --show-current-patch
 
 DESCRIPTION
 -----------
@@ -255,6 +255,11 @@ leave out at most one of A and B, in which case it defaults to HEAD.
 --edit-todo::
 	Edit the todo list during an interactive rebase.
 
+--show-current-patch::
+	Show the current patch in an interactive rebase or when rebase
+	is stopped because of conflicts. This is the equivalent of
+	`git show REBASE_HEAD`.
+
 -m::
 --merge::
 	Use merging strategies to rebase.  When the recursive (default) merge