Made the cache support specifying the block size, breaking the BlobTest.
Made evicter_t not be a friend of page_t.  Now it is a frenemy.
Fixed errors in the BlobTest (bugs in prepend related to specifying the ser buf size -- there were no bugs applicable to the rdb protocol).
Merge branch 'next' into sam_alt_block_size
Made page_t::hypothetical_memory_usage be const.
Merge branch 'sam_alt_block_size' into next