Allow unions of table types with the same name but from different namespaces.

Also fixed most codegenerators using the wrong namespace when multiple
namespace were used in a file, with some files not being generated.

Change-Id: Ib42969221239d7244e431cbd667ef69200fc415f
Tested: on Linux.
Bug: 29338474

tests/namespace_test/NamespaceC/TableInC.py

@@ -0,0 +1,39 @@
+# automatically generated by the FlatBuffers compiler, do not modify
+
+# namespace: NamespaceC
+
+import flatbuffers
+
+class TableInC(object):
+    __slots__ = ['_tab']
+
+    # TableInC
+    def Init(self, buf, pos):
+        self._tab = flatbuffers.table.Table(buf, pos)
+
+    # TableInC
+    def ReferToA1(self):
+        o = flatbuffers.number_types.UOffsetTFlags.py_type(self._tab.Offset(4))
+        if o != 0:
+            x = self._tab.Indirect(o + self._tab.Pos)
+            from .TableInFirstNS import TableInFirstNS
+            obj = TableInFirstNS()
+            obj.Init(self._tab.Bytes, x)
+            return obj
+        return None
+
+    # TableInC
+    def ReferToA2(self):
+        o = flatbuffers.number_types.UOffsetTFlags.py_type(self._tab.Offset(6))
+        if o != 0:
+            x = self._tab.Indirect(o + self._tab.Pos)
+            from .SecondTableInA import SecondTableInA
+            obj = SecondTableInA()
+            obj.Init(self._tab.Bytes, x)
+            return obj
+        return None
+
+def TableInCStart(builder): builder.StartObject(2)
+def TableInCAddReferToA1(builder, referToA1): builder.PrependUOffsetTRelativeSlot(0, flatbuffers.number_types.UOffsetTFlags.py_type(referToA1), 0)
+def TableInCAddReferToA2(builder, referToA2): builder.PrependUOffsetTRelativeSlot(1, flatbuffers.number_types.UOffsetTFlags.py_type(referToA2), 0)
+def TableInCEnd(builder): return builder.EndObject()