FORGE-554 Provide options for autocomplete relative to the typed paths.

The fix was to ensure that PathspecParser computed the options relative
to the supplied path instead of the drive root.

Also fixed a bug involving display and usage of forward slashes instead
of the OS file separators when displaying the paths or accepting them as
user input in Windows.

shell-api/src/main/java/org/jboss/forge/shell/util/PathspecParser.java

@@ -104,7 +104,7 @@ else if (path.startsWith("~"))
       // for windows, support drive letter prefixes here.
       else if (isWindows && path.matches("^[a-zA-Z]{1,1}:(/|\\\\).*"))
       {
-         int idx = path.indexOf(slashChar) + 1;
+         int idx = path.lastIndexOf(slashChar) + 1;
          r = new DirectoryResource(factory, new File(path.substring(0, idx)).getAbsoluteFile());
          cursor = idx;
       }

shell/src/main/java/org/jboss/forge/shell/completer/OptionValueResolverCompleter.java

@@ -187,10 +187,10 @@ else if (valueMap.get(option) == null)
       for (Resource<?> r : new PathspecParser(resourceFactory, shell.getCurrentResource(), val + "*")
                .resolve())
       {
-         // Add result to the results list, and append a '/' if the
+         // Add result to the results list, and append a file separator ('/' or '\\') if the
          // resource has children.
-         String name = ("~".equals(val) ? "~/" : "") + r.getName()
-                  + (r.isFlagSet(ResourceFlag.Node) ? "/" : "");
+         String name = ("~".equals(val) ? "~" + File.separator : "") + r.getName()
+                  + (r.isFlagSet(ResourceFlag.Node) ? File.separator : "");
          results.add(name);
       }