REVIEW-3910: Better support for parsing c-source files like the c-prepreprocessor
- Handle line-continuation characters
- Convert /* comments */ to single character
    - Commented out includes are not processed
- #include directive in quotes not processed
Return unknown includes/imports out of CSourceParser
- This will allow us to detect #include MY_DEF
REVIEW-3910: A directory cannot satisfy a #include dependency
REVIEW-3910: Consider a C source/header changed if it provides a MACRO to #include
REVIEW-3910: Clear environment variables when executing with VisualC++ tools
REVIEW-3910: Added a couple of review items to the spec
Checkstyle fix