attr: convert git_all_attrs() to use "struct attr_check"

This updates the other two ways the attribute check is done via an
array of "struct attr_check_item" elements.  These two niches
appear only in "git check-attr".

 * The caller does not know offhand what attributes it wants to ask
   about and cannot use attr_check_initl() to prepare the
   attr_check structure.

 * The caller may not know what attributes it wants to ask at all,
   and instead wants to learn everything that the given path has.

Such a caller can call attr_check_alloc() to allocate an empty
attr_check, and then call attr_check_append() to add attribute names
one by one.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/attr.h b/attr.h
index e611b13..9f27298 100644
--- a/attr.h
+++ b/attr.h
@@ -56,13 +56,10 @@ int git_check_attrs(const char *path, int, struct attr_check_item *);
 extern int git_check_attr(const char *path, struct attr_check *check);
 
 /*
- * Retrieve all attributes that apply to the specified path.  *num
- * will be set to the number of attributes on the path; **check will
- * be set to point at a newly-allocated array of git_attr_check
- * objects describing the attributes and their values.  *check must be
- * free()ed by the caller.
+ * Retrieve all attributes that apply to the specified path.
+ * check holds the attributes and their values.
  */
-int git_all_attrs(const char *path, int *num, struct attr_check_item **check);
+extern void git_all_attrs(const char *path, struct attr_check *check);
 
 enum git_attr_direction {
 	GIT_ATTR_CHECKIN,