Refactorization in CheckNullPointer:
- Use AST to detect dereferences
- Added more unit tests
- Removed handling of unknown constructs in CheckNullPointer::isPointerDeRef()

Added link to verbose message cstyleCast.
Use AST in CheckIO::checkCoutCerrMisusage() - fixes #3254.
Enhancements related to duplicate expression checking:
- Fixed astIsFloat() for complex expressions
- Enhanced support for commutative operators (#5260)
Fixed CID 1192595: Dereference null return value in checkother.
Fixed CID 1037101 Dereference after null check in ExecutionPath::checkScope.
travis: more checks.