clarified modules;

--- a/src/Tools/VSCode/extension/src/extension.ts	Tue May 30 14:43:42 2017 +0200
+++ b/src/Tools/VSCode/extension/src/extension.ts	Tue May 30 15:29:42 2017 +0200
@@ -69,7 +69,7 @@
       if (editor) {
         const uri = editor.document.uri
         const cursor = editor.selection.active
-        if (uri.scheme === "file" && cursor)
+        if (library.is_file(uri) && cursor)
           caret_update = { uri: uri.toString(), line: cursor.line, character: cursor.character }
       }
       if (last_caret_update !== caret_update) {

--- a/src/Tools/VSCode/extension/src/library.ts	Tue May 30 14:43:42 2017 +0200
+++ b/src/Tools/VSCode/extension/src/library.ts	Tue May 30 15:29:42 2017 +0200
@@ -1,7 +1,7 @@
 'use strict';
 
 import * as os from 'os';
-import { ViewColumn, TextEditor, workspace } from 'vscode'
+import { ViewColumn, TextEditor, Uri, workspace } from 'vscode'
 
 
 /* platform information */
@@ -12,6 +12,14 @@
 }
 
 
+/* file URIs */
+
+export function is_file(uri: Uri): boolean
+{
+  return uri.scheme === "file"
+}
+
+
 /* Isabelle configuration */
 
 export function get_configuration<T>(name: string): T