internally keep multiple applications of the same markers as separate

entities such that the new iter() API can iterate over pytest.mark
function attributes, getting all such applications.  See added example
for more info.

testing/test_mark.py

@@ -230,6 +230,14 @@ class TestFunctional:
         assert marker.args == ("pos0", "pos1")
         assert marker.kwargs == {'x': 3, 'y': 2, 'z': 4}
 
+        # test the new __iter__ interface
+        l = list(marker)
+        assert len(l) == 3
+        assert l[0].args == ("pos0",)
+        pytest.xfail(reason="needs reordering of parametrize transfermarks")
+        assert l[1].args == ()
+        assert l[2].args == ("pos1", )
+
     def test_mark_other(self, testdir):
         pytest.raises(TypeError, '''
             testdir.getitem("""
@@ -259,6 +267,23 @@ class TestFunctional:
             "keyword: *hello*"
         ])
 
+    def test_merging_markers_two_functions(self, testdir):
+        p = testdir.makepyfile("""
+            import pytest
+            @pytest.mark.hello("pos1", z=4)
+            @pytest.mark.hello("pos0", z=3)
+            def test_func(self):
+                pass
+        """)
+        items, rec = testdir.inline_genitems(p)
+        item, = items
+        keywords = item.keywords
+        marker = keywords['hello']
+        l = list(marker)
+        assert len(l) == 2
+        assert l[0].args == ("pos0",)
+        assert l[1].args == ("pos1",)
+
 
 class TestKeywordSelection:
     def test_select_simple(self, testdir):