Allow basho_bench to pre-compute and pre-load Riak vnode data dirs.

Currently this only works with the eleveldb driver.  For maximum
utility, it should be extended to work with bitcask and other
Riak backends.
Add comments to examples/shortcut.config
Add support for Bitcask

Test method:

* Use the `examples/shortcut.config` file as shown to pre-populate 50K keys.
  Change the `code_paths` and `shortcut_data_dir` to reflect your
  environment.
* Run `./basho_bench ./examples/shortcut.config`
* Over on a Riak console, use:
  * {ok, C} = riak:local_client().
  * [ok] = lists:usort([catch element(1, C:get(<<"b1">>, <<X:32/native>>)) || X <- lists:seq(0,49999)]).
Add support for experimental hanoidb storage manager
Refactor preflist calculation, clean up debugging cruft
verify seq_int resume value is not out of bounds
Updated http_raw driver to allow appending custom headers in the .config file, which is useful for things like HTTP Auth.
Add additional configuration items to basho_bench_driver_riakc_pb.erl

* pb_connect_options, list(two_tuple()), list of valid Protocol Buffers
  client connection options.
  Default = [{auto_reconnect, true}]

NOTE: The new default value creates a change in behavior of the
      PB client: the default is {auto_reconnect, false}.  Users
      of the PB client that wish the old & brittle behavior of
      crashing on server-side errors, timeouts, etc. must provide
      explicit configuration now to disable auto_reconnect behavior.

* pb_timeout_general, integer(), overall single Protocol Buffer
  operation timeout value.
  Default = 62000
  Units = milliseconds

* pb_timeout_read, integer(), overall single Protocol Buffer
  read operation timeout value.
  Default = value of pb_timeout_general
  Units = milliseconds

* pb_timeout_write, integer(), overall single Protocol Buffer
  write operation timeout value.
  Default = value of pb_timeout_general
  Units = milliseconds

* pb_timeout_listkeys, integer(), overall single Protocol Buffer
  listkeys operation timeout value.
  Default = value of pb_timeout_general
  Units = milliseconds

* pb_timeout_mapreduce, integer(), overall single Protocol Buffer
  mapreduce operation timeout value.
  Default = value of pb_timeout_general
  Units = milliseconds
Merge of branch  slf-bulk-insert-shortcut2
Merge pull request #68 from joecaswell/jhc-resumecheck

verify seq_int resume value is not out of bounds
Merge pull request #69 from nathanaschbacher/master

Updated http_raw driver to allow appending custom headers.
Address review request for example config
Address review request for 'update' error handling
Add riak_cs support (imported from riak_cs/bench)
Add option '-u UNIT' for changing unit of measure in gp_throughput.sh
Add more comments to riakc_pb.config
Merge branch 'slf-pb-driver-additional-config'
Merge pull request #78 from sogabe/riak_cs_2

Add riak_cs support (imported from riak_cs/bench)
Merge pull request #79 from sogabe/gp_throughput_unit

Add option '-u UNIT' for changing unit of measure in gp_throughput.sh
Enable kernel poll by default