Merge branch 'dt/refs-pseudo'

To prepare for allowing a different "ref" backend to be plugged in
to the system, update_ref()/delete_ref() have been taught about
ref-like things like MERGE_HEAD that are per-worktree (they will
always be written to the filesystem inside $GIT_DIR).

* dt/refs-pseudo:
  pseudoref: check return values from read_ref()
  sequencer: replace write_cherry_pick_head with update_ref
  bisect: use update_ref
  pseudorefs: create and use pseudoref update and delete functions
  refs: add ref_type function
  refs: introduce pseudoref and per-worktree ref concepts

refs.h

@@ -445,6 +445,14 @@ extern int parse_hide_refs_config(const char *var, const char *value, const char
 
 extern int ref_is_hidden(const char *);
 
+enum ref_type {
+	REF_TYPE_PER_WORKTREE,
+	REF_TYPE_PSEUDOREF,
+	REF_TYPE_NORMAL,
+};
+
+enum ref_type ref_type(const char *refname);
+
 enum expire_reflog_flags {
 	EXPIRE_REFLOGS_DRY_RUN = 1 << 0,
 	EXPIRE_REFLOGS_UPDATE_REF = 1 << 1,