Added reliable way for finding out if an entry is a directory for ms-dos and unix container creator's systems.

Sources/ZipContainer.swift

@@ -81,7 +81,14 @@ public class ZipEntry: ContainerEntry {
      Particularly, it is true if size of data is 0 and last character of entry's name is '/'.
     */
     public var isDirectory: Bool {
-        return self.size == 0 && self.name.characters.last == "/"
+        let hostSystem = (cdEntry.versionMadeBy & 0xFF00) >> 8
+        if hostSystem == 0 || hostSystem == 3 { // MS-DOS or UNIX case.
+            // In both of this cases external file attributes indicate if this is a directory.
+            // This is indicated by a special bit in the lowest byte of attributes.
+            return cdEntry.externalFileAttributes & 0x10 != 0
+        } else {
+            return size == 0 && name.characters.last == "/"
+        }
     }
 
     /**