and compressed tables

buf_LRU_drop_page_hash_for_tablespace(): after releasing and
reacquiring the buffer pool mutex, do not dereference any block
descriptor pointer that is not known to be a pointer to an
uncompressed page frame (type buf_block_t; state ==
BUF_BLOCK_FILE_PAGE). Also, defer the acquisition of the block_mutex
until it is needed.

buf_page_get_gen(): Add mode == BUF_GET_IF_IN_POOL_PEEK for
buffer-fixing a block without making it young in the LRU list.

buf_page_get_gen(), buf_page_init(), buf_LRU_block_remove_hashed_page():
Set bpage->state = BUF_BLOCK_ZIP_FREE before buf_buddy_free(bpage),
so that similar race conditions might be detected a little easier.

btr_search_drop_page_hash_when_freed(): Use BUF_GET_IF_IN_POOL_PEEK
when dropping the hash indexes.

rb://528 approved by Jimmy Yang