Adding more details when logging dependencies errors.

Testing for `dependentFile` exitence is not needed, because it is implied by the already present condition `inputFile.outputFile !== outputFile` (line 54).
It is true that, line 83, I pass null for the `dependentFile` argument, but this only happens for the first level of calls, which means, for the files which are in the `outputFile` package (for which `inputFile` is part of `outputFile.sourceFiles`, which implies `inputFile.outputFile === outputFile`).