Fix: svg import ignores rectangle radius when only one side is set.

This follows the SVG spec in which only one side can be set and set the other
side to the same value in this case.
This also adds support for percent values.

Fixes paperjs#1863

src/svg/SvgImport.js

@@ -281,11 +281,25 @@ new function() {
 
         // https://www.w3.org/TR/SVG/shapes.html#RectElement
         rect: function(node) {
+            var rx = SvgElement.get(node, 'rx');
+            var ry = SvgElement.get(node, 'ry');
+            if (rx === null && ry !== null) {
+                rx = ry;
+            } else if (ry === null && rx !== null) {
+                ry = rx;
+            }
+            if (/%\s*$/.test(rx)) {
+                rx = parseFloat(rx) * rootSize.width / 100;
+            }
+            if (/%\s*$/.test(ry)) {
+                ry = parseFloat(ry) * rootSize.height / 100;
+            }
+            var radius = rx !== null && ry !== null ? new Size(rx, ry) : null;
             return new Shape.Rectangle(new Rectangle(
                         getPoint(node),
                         getSize(node)
-                    ), getSize(node, 'rx', 'ry'));
-            },
+                    ), radius);
+        },
 
         // https://www.w3.org/TR/SVG/shapes.html#LineElement
         line: function(node) {

test/tests/SvgImport.js

@@ -205,7 +205,8 @@ if (!isNodeContext) {
         'gradients-1': {},
         'gradients-2': !isPhantomContext && {},
         'gradients-3': {},
-        'gradients-4': {}
+        'gradients-4': {},
+        'rectangles': {}
     };
     Base.each(svgFiles, function(options, name) {
         if (options) {