Teach 'git pull' about --rebase

When calling 'git pull' with the '--rebase' option, it performs a
fetch + rebase instead of a fetch + merge.

This behavior is more desirable than fetch + pull when a topic branch
is ready to be submitted and needs to be update.

fetch + rebase might also be considered a better workflow with shared
repositories in any case, or for contributors to a centrally managed
repository, such as WINE's.

As a convenience, you can set the default behavior for a branch by
defining the config variable branch.<name>.rebase, which is
interpreted as a bool.  This setting can be overridden on the command
line by --rebase and --no-rebase.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -346,6 +346,13 @@ branch.<name>.mergeoptions::
 	option values containing whitespace characters are currently not
 	supported.
 
+branch.<name>.rebase::
+	When true, rebase the branch <name> on top of the fetched branch,
+	instead of merging the default branch from the default remote.
+	*NOTE*: this is a possibly dangerous operation; do *not* use
+	it unless you understand the implications (see gitlink:git-rebase[1]
+	for details).
+
 clean.requireForce::
 	A boolean to make git-clean do nothing unless given -f
 	or -n.   Defaults to true.

Documentation/git-pull.txt

@@ -33,6 +33,16 @@ include::urls-remotes.txt[]
 
 include::merge-strategies.txt[]
 
+\--rebase::
+	Instead of a merge, perform a rebase after fetching.
+	*NOTE:* This is a potentially _dangerous_ mode of operation.
+	It rewrites history, which does not bode well when you
+	published that history already.  Do *not* use this option
+	unless you have read gitlink:git-rebase[1] carefully.
+
+\--no-rebase::
+	Override earlier \--rebase.
+
 DEFAULT BEHAVIOUR
 -----------------