Merge branch 'bf/fetch-set-head-config'

"git fetch" honors "remote.<remote>.followRemoteHEAD" settings to
tweak the remote-tracking HEAD in "refs/remotes/<remote>/HEAD".

* bf/fetch-set-head-config:
  remote set-head: set followRemoteHEAD to "warn" if "always"
  fetch set_head: add warn-if-not-$branch option
  fetch set_head: move warn advice into advise_if_enabled
  fetch: add configuration for set_head behaviour

Documentation/config/remote.txt

@@ -101,6 +101,19 @@ remote.<name>.serverOption::
 	The default set of server options used when fetching from this remote.
 	These server options can be overridden by the `--server-option=` command
 	line arguments.
+
+remote.<name>.followRemoteHEAD::
+	How linkgit:git-fetch[1] should handle updates to `remotes/<name>/HEAD`.
+	The default value is "create", which will create `remotes/<name>/HEAD`
+	if it exists on the remote, but not locally, but will not touch an
+	already existing local reference. Setting to "warn" will print
+	a message if the remote has a different value, than the local one and
+	in case there is no local reference, it behaves like "create".
+	A variant on "warn" is "warn-if-not-$branch", which behaves like
+	"warn", but if `HEAD` on the remote is `$branch` it will be silent.
+	Setting to "always" will silently update it to the value on the remote.
+	Finally, setting it to "never" will never change or create the local
+	reference.
 +
 This is a multi-valued variable, and an empty value can be used in a higher
 priority configuration file (e.g. `.git/config` in a repository) to clear