Renamed "_unix.go" files to "_linux.go"

The go compiler doesn't feature a build constraint for Unix per se, therefore it treats the *_unix.go as any other file and builds them regardless the OS. This lead to some conflicts when attempting to build under Windows (namely, the compiler yelled because of test suites declared twice), but all seemed well under Linux(as the appropriately tagged _windows.go files were ignored in the first place and no conflicts occurred).

Now the package should build successfully under Windows as well and no conflicts signaled.