Optimize committers/users map retrieval for statistic graphs (#13487).

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extra : convert_revision : svn%3Ae93f8b46-1217-0410-a6f0-8f06a7374b81/trunk%4013361
Fix syntax for ruby 1.8.7 (#13487).

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extra : convert_revision : svn%3Ae93f8b46-1217-0410-a6f0-8f06a7374b81/trunk%4013362