Import proto (without java_package) from another package

[davidlar]

In version 1.4.0, importing from another package doesn't work anymore if java_package is undefined in the imported file. java_package should default to proto package according to spec.

I have also done some fixes in the test code (filename case and line endings) so it will succeed in Linux as well. Some testcases wrote their output to src/test/resources and wrote over the example files. When they later compared the generated files with the example files, it was the same files and it would always succeed. I moved output dir to target to solve that.