* path = Canonical absolute path
* prefix_list = Colon-separated list of absolute paths
*
- * Determines, for each path in parent_list, whether the "prefix" really
+ * Determines, for each path in prefix_list, whether the "prefix" really
* is an ancestor directory of path. Returns the length of the longest
* ancestor directory, excluding any trailing slashes, or -1 if no prefix
* is an ancestor. (Note that this means 0 is returned if prefix_list is