Occasionally compact combined state on write.

This is needed to avoid arbitrarily large blowup
for many-element windows.  Now, with a fixed
probability (currently 0.2%) when writing the state,
instead of doing a blind write we read in all
accumulated values, combine, and replace everything
with the final combined value.

----Release Notes----
[]
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=109239045

Version management

Declare version 1.2.0. Prepare for version 1.2.1.

----Release Notes----
[]
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=104700491

Handle exceptions from within the SDK while processing work

The DataflowWorkerHarness when processing work wasn't handling
general exceptions from being thrown causing the processing
threads to all die leaving a zombie worker.
----Release Notes----

[]
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=104664789

Updates dependency google-api-services-datastore-protobuf.

----Release Notes----
Updating dependency google-api-services-datastore-protobuf from v1beta2-rev1-2.1.2 to v1beta2-rev1-3.0.2.

[]
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=103114238

Dataflow GA: update GitHub's README.md to remove Beta language

----Release Notes----
[]
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=100331508

Move GroupByKey validation into validate method

----Release Notes----
Re-enabled verification of GroupByKey usage. Specififically, the key
must have a deterministic coder and using GroupByKey with an Unbounded
PCollection requires windowing or triggers.

[]
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=99194010

Version 0.4.20150710

Change ExpectedLogs to include better stack-traces

Also add support for verifying the absence of a message.

----Release Notes----

[]
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=94922273

Update README.md for Beta

Change the ENVIRONMENT_MAJOR_VERSION to "1"

----Release Notes----
[]
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=89562565