Refactor ad hoc string and file comparison test code into helper functions.

CL=50959312
DATE=2013/08/16
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=50959312
Plumb a context parameter through the frontend and to the backend for RPC tracing.

CL=51066769
DATE=2013/08/19
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=51066769