Remove obsolete Alter query builder. Alter is performed by raw backstore
without query builder related code.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=79451419
Implement parameter binding in SELECT's search conditions.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=79698604
Add backstore design doc.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=79708375
Add parameter binding for DELETE queries.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=79710509
Rename classes for better readability.

lf.query.Context -> lf.query.Builder
lf.query.QueryBuilder -> lf.query.BaseBuilder
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=79714670
Adding new ObserverRegistry class.

The new class provides a mechanism for
- keeping track of all observed queries and last known results.
- registering/unreristering observed queries.

The new mechanism will be hooked up to other components in follow up CLs.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=79787916
Remove lf.query.Query typedef and templatize lf.query.BaseBuilder to
have stricter type coverage checks.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=79799591