update 1.4 branch with prefetch fix and global options loading
activate fadvise_willneed and write_threads options
add iterators.erl file that test mv-iterator-prev code.  update build_deps.sh
Add defensive check of arity on all option parser usage of enif_get_tuple().  Will add same in other routines later.
missed some conflicts.
point build_deps to leveldb equivalent branch
merge of develop and mv-fadvise-control-2.0