Merge branch 'maint'

* maint:
  sha1_file.c: resolve confusion EACCES vs EPERM
  sha1_file: avoid bogus "file exists" error message
  git checkout: don't warn about unborn branch if -f is already passed
  bash: offer refs instead of filenames for 'git revert'
  bash: remove dashed command leftovers
  git-p4: fix keyword-expansion regex
  fast-export: use an unsorted string list for extra_refs
  Add new testcase to show fast-export does not always exports all tags

builtin-checkout.c

@@ -553,7 +553,7 @@ static int switch_branches(struct checkout_opts *opts, struct branch_info *new)
 	if (!opts->quiet && !old.path && old.commit && new->commit != old.commit)
 		describe_detached_head("Previous HEAD position was", old.commit);
 
-	if (!old.commit) {
+	if (!old.commit && !opts->force) {
 		if (!opts->quiet) {
 			fprintf(stderr, "warning: You appear to be on a branch yet to be born.\n");
 			fprintf(stderr, "warning: Forcing checkout of %s.\n", new->name);