Update tools.mk to the latest.
Fix 'undefined' bucket type issue.

This was broken by #970. The client is not required to send a
bucket-type in the request, therefore it can be the atom 'undefined',
which corresponds to the "default" bucket-type. Also untangled the
logic into a separate "check" for the presence of the bucket-type.

This was found by the Python client suite here:
http://buildbot.bos1/builders/python-client-test/builds/60/steps/make%20test/logs/stdio
The 'stream' field can be undefined as well as true/false.
Add type specs for new functions in riak_kv_pb_bucket
Merge pull request #974 from basho/bugfix/sdc/bucket-type-kl-bl

Fix 'undefined' bucket type issue.

Reviewed-by: kellymclaughlin