Fix #168 and #169: Rationalize 'Connection.delete_entities'

[tseaver]

Please review this after PR #253 (it is based on that branch).

Fixes #168 and #169.

Supersedes PR #256.

[coveralls]

Coverage remained the same when pulling 8ebace3 on tseaver:168_169-connection_delete_entities into 906700b on GoogleCloudPlatform:master.

[tseaver]

Merged from the trunk: the earlier changesets (from PR #253) are now gone from the diff.

[dhermes]

Can you rebase instead of merging so as not to introduce unnecessary commits into our history?

[coveralls]

Coverage remained the same when pulling 63b08a5 on tseaver:168_169-connection_delete_entities into 83e8262 on GoogleCloudPlatform:master.

[tseaver]

Rebasing an already-shared branch is not part of my normal workflow. After reading up here and here, I've tried the rebase as:

$ git checkout 168_169-connection_delete_entities
$ git rebase master
$ git push -f   # douche chill

[coveralls]

Coverage remained the same when pulling 7e134d3 on tseaver:168_169-connection_delete_entities into 83e8262 on GoogleCloudPlatform:master.

[dhermes]

Overall LGTM.

It seems strange to have delete_entities defined on Connection. That strangeness isn't dealt with here, but is worth discussing / potentially filing a follow up bug to refactor.

[tseaver]

Rebased to resolve merge conflicts.

[tseaver]

WRT "strangeness": note that the connection mediates all mutations passed to the backend (saves, deletes, commits). Loading / storing / deleting entities is basically its only responsibility.

[coveralls]

Coverage remained the same when pulling e8dda0f on tseaver:168_169-connection_delete_entities into 20ac9ef on GoogleCloudPlatform:master.