Added unit test for referenced parent selectors

Name: Parent selectors not working within mixins using (reference)
Number: #1979

test/css/import-reference.css

@@ -74,3 +74,9 @@ div#id.class[a=1][b=2].class:not(1) {
     color: red;
   }
 }
+.test {
+  color: red;
+}
+.test:first-child {
+  color: blue;
+}

test/less/import-reference.less

@@ -19,3 +19,4 @@
 
 .class:extend(.class all) {
 }
+.mixin-with-nested-selectors();

test/less/import/import-reference.less

@@ -49,7 +49,7 @@
     color: red;
   }
 }
-
+//https://github.com/less/less.js/issues/2359
 @supports (something: else) {
   .class {
     something: else;
@@ -63,3 +63,12 @@
     something: else;
   }
 }
+//https://github.com/less/less.js/issues/1979
+.mixin-with-nested-selectors() {
+  .test {
+    color: red;
+    &:first-child {
+      color: blue;
+    }
+  }
+}