Merge branch 'nd/clone-detached'

* nd/clone-detached:
  clone: fix up delay cloning conditions
  push: do not let configured foreign-vcs permanently clobbered
  clone: print advice on checking out detached HEAD
  clone: allow --branch to take a tag
  clone: refuse to clone if --branch points to bogus ref
  clone: --branch=<branch> always means refs/heads/<branch>
  clone: delay cloning until after remote HEAD checking
  clone: factor out remote ref writing
  clone: factor out HEAD update code
  clone: factor out checkout code
  clone: write detached HEAD in bare repositories
  t5601: add missing && cascade

advice.c

@@ -73,3 +73,17 @@ void NORETURN die_resolve_conflict(const char *me)
 	error_resolve_conflict(me);
 	die("Exiting because of an unresolved conflict.");
 }
+
+void detach_advice(const char *new_name)
+{
+	const char fmt[] =
+	"Note: checking out '%s'.\n\n"
+	"You are in 'detached HEAD' state. You can look around, make experimental\n"
+	"changes and commit them, and you can discard any commits you make in this\n"
+	"state without impacting any branches by performing another checkout.\n\n"
+	"If you want to create a new branch to retain commits you create, you may\n"
+	"do so (now or later) by using -b with the checkout command again. Example:\n\n"
+	"  git checkout -b new_branch_name\n\n";
+
+	fprintf(stderr, fmt, new_name);
+}