refs leafo#134, refs leafo#137 - add test case from @smuuf

Author: robocoder

tests/inputs/import.scss

@@ -16,3 +16,8 @@ code {
 }
 
 @import "imports/partial";
+
+body {
+    color: $variable;
+    @include partial-mixin();
+}

tests/inputs/imports/_partial.scss

@@ -3,4 +3,8 @@
     color: blue;
 }
 
+$variable: #7C2;
 
+@mixin partial-mixin() {
+    background: gray;
+}

tests/outputs/import.css

@@ -21,3 +21,7 @@ code div {
 
 #partial {
   color: blue; }
+
+body {
+  color: #7c2;
+  background: gray; }