fix(autocomplete): fixes z-index issues with autocomplete menu

Author: Robert Messerle

src/components/autocomplete/autocomplete.scss

@@ -68,6 +68,9 @@ md-autocomplete {
     position: relative;
     overflow: visible;
     height: 40px;
+    &.md-menu-showing {
+      z-index: $z-index-backdrop + 1;
+    }
     md-progress-linear[md-mode=indeterminate] {
       position: absolute;
       bottom: 0; left: 0; width: 100%;

src/components/autocomplete/js/autocompleteDirective.js

@@ -132,7 +132,7 @@ function MdAutocomplete ($mdTheming, $mdUtil) {
       return '\
         <md-autocomplete-wrap\
             layout="row"\
-            ng-class="{ \'md-whiteframe-z1\': !floatingLabel }"\
+            ng-class="{ \'md-whiteframe-z1\': !floatingLabel, \'md-menu-showing\': !$mdAutocompleteCtrl.hidden }"\
             role="listbox">\
           ' + getInputElement() + '\
           <md-progress-linear\