Allow streaming results from list-buckets in the fsm.
Expose the timeout option by itself on riak_client:list_buckets().
pre-rebase
add timeouts to listing operations
- rework the riak_client interface a little
- add streaming option & timeout to list buckets
- add timeout to list keys
remove functional test posing as unit test, functional tests
exists now in riak_test
add more backwards compatability support.  by default, use the old
path, unless the client specifies streaming.
reduce code duplication
add a default timeout for the case where none is supplied.
Merge pull request #527 from basho/sdc-list-buckets-timeout

List buckets timeout & streaming