use path separator for project path

Author: Vladimir Kotal

opengrok-indexer/src/main/java/org/opengrok/indexer/index/Indexer.java

@@ -898,7 +898,7 @@ public void prepareIndexer(RuntimeEnvironment env,
             // Add a project for each top-level directory in source root.
             for (File file : files) {
                 String name = file.getName();
-                String path = "/" + name;
+                String path = File.separator + name;
                 if (oldProjects.containsKey(name)) {
                     // This is an existing object. Reuse the old project,
                     // possibly with customizations, instead of creating a