CheckLocalHash - check mtime if size differs as well
CheckLocalHash  - try open file only if we check treehash (i.e. when size same)
CheckLocalHash - existance test
CheckLocalHash - test refactor
CheckLocalHash - more refactor
CheckLocalHash - tests - more robust file existance check
CheckLocalHash - tests - more robust file size check
CheckLocalHash - tests - more robust file mtime check
CheckLocalHash - tests - more robust file open mock
CheckLocalHash - tests - more robust treehash mocks
CheckLocalHash - test - dont check mtime if it does not exit