Automated g4 rollback of changelist 82274926.

*** Reason for rollback ***

Broke a variety of projects.

*** Original change description ***

Treat "?T" the same as "T|null", even if T is a template type.

***
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=82280995
Remove usage of raw HashSet
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=82335628