582906 XSD validating multiple imports of the same schema

* xmlschemas.c: When validating a schema that includes the same file
  that has no targetNamespace defined an internal erro was thrown,
  depending on the orig namespace that should be allowed though
* test/schemas/582906-* result/schemas/582906-*: 2 tests case, one
  where this is allowed, and one where this is forbidden
diff --git a/test/schemas/582906-2_0.xml b/test/schemas/582906-2_0.xml
new file mode 100644
index 0000000..e928957
--- /dev/null
+++ b/test/schemas/582906-2_0.xml
@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<CollectedOutput xmlns="http://example.com/xml/Aggregator"
+             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+             xsi:schemaLocation="http://example.com/xml/Aggregator
+             582906-2-0.xsd">5.3</CollectedOutput>