feat(url parser): better error message for slash in hostname

ported from #1559

Author: Jessica Lord

lib/url_parser.js

@@ -198,7 +198,13 @@ function parseConnectionString(url, options) {
   for (i = 0; i < hosts.length; i++) {
     var r = parser.parse(f('mongodb://%s', hosts[i].trim()));
     if (r.path && r.path.indexOf(':') !== -1) {
-      throw new Error('Double colon in host identifier');
+      // Not connecting to a socket so check for an extra slash in the hostname.
+      // Using String#split as perf is better than match.
+      if (r.path.split('/').length > 1 && r.path.indexOf('::') === -1) {
+        throw new Error('Slash in host identifier');
+      } else {
+        throw new Error('Double colon in host identifier');
+      }
     }
   }