Made garbage_bytes, token_bytes, index_bytes use non-ceil-aligned block sizes.
Made num_writes param and variables be size_t.
Removed useless whitespace in young_extent_queue declaration.
Moved gc_entry_t declaration to data_block_manager.cc.
Moved a few types out of the data_block_manager_t class in prep for including the header file less places.
Removed dead code gc_disable/gc_enable functionality.