fixed canonicalize_pathname() breakage: fixed str_move() function (memmove semantics...

fixed canonicalize_pathname() breakage: fixed str_move() function (memmove semantics) again

This patch reintroduces fix firstly appeared in (and recently broken by mhl revert)
>   commit e48cb7c89ff3e54de70130a3de2136a9902a023d
>   Author: Sergei Trofimovich <st@anti-virus.by>
>   Date:   Fri Jan 30 09:31:28 2009 +0200
>
>        mhl: added mhl_strmove() function (memmove semantics)
...
>            Snippet of man strcpy:
>       DESCRIPTION
>               The  strcpy()  function copies the string pointed to by src, including the terminating
>               null byte ('\0'), to the buffer pointed to by dest.  ___The strings may not overlap___,
>               and the destination string dest must be  large enough to receive the copy.
>       We used strcpy to move data chunk in memory: "./foo" -> "foo", etc.
>
>       This patch introduces mhl_strmove and fixed canonicalize_pathname.

Signed-off-by: Sergei Trofimovich <slyfox@inbox.ru>