This updates CPPLintTool to subclass the newer BaseTool, and to use

the newer features it offers (dependencies, improved file extension

handling, centralized base command building, and standardized error code

output).
The new version of the tool has less verbose, safer output parsing. Both

the old and new versions used a regex, but the new one is designed to

better fit with the output from the tool, and to avoid a bunch of

now-unnecesary processing.

Unit tests pass for Python 2.7 and 3.x.