+ The algorithm is in spirit similar to the one described in rfc1808,
+ although implemented differently, in one pass. To recap, path
+ elements containing only "." are removed, and ".." is taken to mean
+ "back up one element". Single leading and trailing slashes are
+ preserved.
+
+ This function does not handle URL escapes explicitly. If you're
+ passing paths from URLs, make sure to unquote "%2e" and "%2E" to
+ ".", so that this function can find the dots. (Wget's URL parser
+ calls reencode_escapes, which see.)