Prevent removal of metadata elements if they have only text nodes. Also added some unit tests.

unittests/adobe.svg

@@ -7,6 +7,7 @@
      xmlns:ir="http://ns.adobe.com/ImageReplacement/1.0/"     
      xmlns:custom="http://ns.adobe.com/GenericCustomNamespace/1.0/"
      xmlns:xpath="http://ns.adobe.com/XPath/1.0/"
+     xmlns:ok="A.namespace.we.want.left.in"
      i:viewOrigin="190.2959 599.1841" i:rulerOrigin="0 0" i:pageBounds="0 792 612 0">
 <x:foo>bar</x:foo>
 <i:foo>bar</i:foo>
@@ -26,4 +27,18 @@
 	<slices/>
 	<sliceSourceBounds y="191.664" x="190.296" width="225.72" height="407.52" bottomLeftOrigin="true"/>
 </sfw>
+<rect width="300" height="200" fill="green"
+	x:baz="1"
+	i:baz="1"
+	graph:baz="1"
+	a:baz="1"
+	f:baz="1"
+	ir:baz="1"
+	custom:baz='1'
+	xpath:baz="1"
+	xmlns:v="http://ns.adobe.Variables/1.0/"
+	v:baz="1"
+	xmlns:sfw="http://ns.adobe.com/SaveForWeb/1.0/"
+	sfw:baz="1"
+	ok:baz="1" />
 </svg>