buf_buddy_alloc_zip(): Calculate the address with char* aritmetics.

buf_buddy_alloc_clean(): Acquire a mutex on the block before
calling buf_LRU_free_block().

buf_buddy_relocate(): Remove the bogus assertion about src and dst
being buddies of each other.  Use mach_read_from_4() instead of
page_get_space_id() and page_get_page_no() to avoid page alignment
assertions.

buf_buddy_free_low(): Replace bogus assertions.