Option to record path coverage using edge coverage

[sears-s]

Note - to clear up the terminology: path coverage is what is being recorded which uses a hash of the edge coverage.

To enable, the edgeCoverageModule option should be set to the name of the module's whose path coverage will be recorded. The view project webpage will show the number of covered paths.

Implementation notes:

• Refactored the patch for drcov and added the option -target_module which enables edge coverage instrumentation and hashing
• The edge coverage hash is parsed from the drcov output (only if the option is enabled) and is included in the TestResult and PutTestResultRequest messages
• Added edge_coverage table which records hashes of edges and the number of executions
• Added column to interesting_testcases that references an entry in the edge_coverage table
• Every testcase result causes LMDatabaseManager::incrementEdgeCoverage() to be called
• Modified signatures for LMDatabaseManager::addEntryToInterestingTestcasesTable(), TestExecutorDynRioSingle(), and TestExecutorDynRio::copyCoveredModulesToDebugExecutionOutput()

Limitations:

• Only supports x86
• Only supports DynamoRIO single mode
• Only supports tracking coverage of one module

Relies on #274.