Merge branch 'nd/maint-autofix-tag-in-head' into maint

* nd/maint-autofix-tag-in-head:
  Accept tags in HEAD or MERGE_HEAD
  merge: remove global variable head[]
  merge: use return value of resolve_ref() to determine if HEAD is invalid
  merge: keep stash[] a local variable

Conflicts:
	builtin/merge.c

commit.h

@@ -38,6 +38,13 @@ struct commit *lookup_commit_reference_gently(const unsigned char *sha1,
 					      int quiet);
 struct commit *lookup_commit_reference_by_name(const char *name);
 
+/*
+ * Look up object named by "sha1", dereference tag as necessary,
+ * get a commit and return it. If "sha1" does not dereference to
+ * a commit, use ref_name to report an error and die.
+ */
+struct commit *lookup_commit_or_die(const unsigned char *sha1, const char *ref_name);
+
 int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long size);
 int parse_commit(struct commit *item);