check Windows file names, e.g. relavant for native Mercurial, but also for Isabelle/Scala;

--- a/src/Pure/Admin/check_sources.scala	Thu Oct 20 13:53:36 2016 +0200
+++ b/src/Pure/Admin/check_sources.scala	Thu Oct 20 16:29:02 2016 +0200
@@ -15,6 +15,9 @@
     val file_pos = path.position
     def line_pos(i: Int) = Position.Line_File(i + 1, file_name)
 
+    if (space_explode('/', Word.lowercase(path.expand.split_ext._1.implode)).contains("aux"))
+      Output.warning("Illegal file-name on Windows" + Position.here(file_pos))
+
     val content = File.read(path)
 
     for { (line, i) <- split_lines(content).iterator.zipWithIndex }