Upgrading version to 0.4.3.

[dhermes]

@tseaver This is just in preparation for cutting a release tomorrow.

I am just going to start writing the release notes and hopefully we can get most of the pending PRs merged before we cut 0.4.3.

---

Using last release PR (#678) as a template.

[dhermes]

With HEAD the current HEAD in this PR:

$ git log 0.4.2..HEAD \
> | grep 'Merge pull request ' \
> | awk -F ' ' '{print $4}' \
> | sort

yields:

#654
#672
#682
#683
#689
#693
#694
#695
#698
#699
#700
#713
#715
#716
#718

---

(UPDATED 10:26am Pacific, 3/13/2015)
#688
#690
#720
#721
#722

[dhermes]

This is my plan for the release notes on the tag:

- Added support for batch requests in storage (GET requests not yet supported).
- [Bugfix][1] in storage ACL methods for incomplete responses.
- Added public `patch()` method on `Blob` and `Bucket`. Requires calling `patch()` to send
  updates rather than doing this under-the-covers when using setters.
- Removing HTTP request when `Blob.properties / Bucket.properties` is accessed. Requires use
  of `_reload_properties` for now (will add a public method shortly).
- Removing `datastore.set_defaults()` from docs: no longer necessary due to
  lazy loading.
- Allowing `storage.get_connection()` to fallback to the default project.
- Adding `storage.lookup_bucket()` which returns a bucket or `None` if
  it doesn't exist (the basic `get_bucket()` throws a `NotFound` / 404
  in this situation).
- Adding `datastore.dataset` to docs.
- Fixing dead-code [reference][2] in datastore `Batch` class.
- Moving `get_all_buckets`, `get_bucket`, `create_bucket` and `delete_bucket` from `Connection` to public functions `storage.get_all_buckets`, etc.
- Swapping the order of `kind` and `dataset_id` in `Query` constructor.
  Allows queries to be constructed as `Query('kind')` (i.e. a
  positional arg can be used).
- Allowing `storage.Batch` to fall back to the implicit connection.
- Making `Bucket.exists()` use `fields` for a smaller payload.

[1]: https://github.com/GoogleCloudPlatform/gcloud-python/pull/682
[2]: https://github.com/GoogleCloudPlatform/gcloud-python/pull/715

[coveralls]

Coverage remained the same at 100.0% when pulling 7a9d5c8 on dhermes:cut-release-0.4.3 into d9e2156 on GoogleCloudPlatform:master.

[dhermes]

@tseaver I'm heading to the airport. WDYT about cutting this release today? I just updated the notes after all the merges this morning (afternoon for you).

[coveralls]

Coverage remained the same at 100.0% when pulling 670caf1 on dhermes:cut-release-0.4.3 into 8173718 on GoogleCloudPlatform:master.

[tseaver]

LGTM for a 0.4.3 release.