Set an explicit 0px border on the map

The JS code which resizes the map relies on being able to parse
the border widths as a number, and by default IE7 seems to have
a border of "medium" which fails to parse.

app/assets/stylesheets/common.css.scss

@@ -383,6 +383,7 @@ h2 {
 
 #map {
   margin: 0px;
+  border: 0px;
   padding: 0px;
 }