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>

unittests/empty-g.svg

@@ -0,0 +1,6 @@
+<svg xmlns="http://www.w3.org/2000/svg">
+  <g/>
+  <g>
+    <rect width="300" height="200" fill="green" />
+  </g>
+</svg>

unittests/empty-metadata.svg

@@ -0,0 +1,3 @@
+<svg xmlns="http://www.w3.org/2000/svg">
+  <metadata></metadata>
+</svg>

unittests/inkscape.svg

@@ -1,5 +1,5 @@
-<svg xmlns="http://www.w3.org/2000/svg" xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:inkscape="dihttp://www.inkscape.org/namespaces/inkscape"
 	inkscape:version="0.46" version="1.0">
 <inkscape:perspective inkscape:vp_x="0 : 526.18109 : 1" inkscape:vp_y="0 : 1000 : 0" inkscape:vp_z="744.09448 : 526.18109 : 1" inkscape:persp3d-origin="372.04724 : 350.78739 : 1" id="perspective3104"/>
-<rect width="300" height="200" fill="green" />
+<rect width="300" height="200" fill="green" inkscape:collect="always"/>
 </svg>

unittests/metadata-with-text.svg

@@ -0,0 +1,3 @@
+<svg xmlns="http://www.w3.org/2000/svg">
+  <metadata>This is a metadata element with only text node children</metadata>
+</svg>