Some trivial pull requests

[Xuesen Liang]

Hello,

Here are some trivial pull requests:

1. remove useless function declaration do_assoc_move_next_bucket()

    https://github.com/memcached/memcached/pull/960

2. declare item_lock_hashpower as a static variable

    https://github.com/memcached/memcached/pull/961

3. remove useless function item_link

    https://github.com/memcached/memcached/pull/962

4. code clean: remove unnecessary argument

    https://github.com/memcached/memcached/pull/965

5. bugfix: size.c: struct size error

    https://github.com/memcached/memcached/pull/968

6. rm_lru_maintainer_initialized

    https://github.com/memcached/memcached/pull/970

7. remove unnecessary HAVE_UNISTD_H check

    https://github.com/memcached/memcached/pull/976

Please take a look and thanks very much!