Added dependency injections for FileUtils and removed redundant code

briar-core/src/org/briarproject/system/FileUtilsImpl.java

@@ -0,0 +1,25 @@
+package org.briarproject.system;
+
+import org.briarproject.api.system.FileUtils;
+
+import java.io.File;
+import java.io.IOException;
+
+public class FileUtilsImpl implements FileUtils {
+
+    public long getTotalSpace(File f) throws IOException {
+        return f.getTotalSpace(); // Requires Java 1.6
+    }
+
+    public long getFreeSpace(File f) throws IOException {
+        return f.getUsableSpace(); // Requires Java 1.6
+    }
+
+    public void deleteFileOrDir(File f) {
+        if (f.isFile())
+            f.delete();
+        else if (f.isDirectory())
+            for (File child : f.listFiles())
+                deleteFileOrDir(child);
+    }
+}