check a feature has a valid start and end

modules/Bio/EnsEMBL/Feature.pm

@@ -124,8 +124,12 @@ sub new {
   }
 
   if(defined($start) && defined($end)) {
-    if($end+1 < $start) {
-      throw('Start must be less than or equal to end+1');
+    if (($start =~ /\d+/) && ($end =~ /\d+/)) {
+      if($end+1 < $start) {
+        throw('Start must be less than or equal to end+1');
+      }
+    } else {
+      throw('Start and end must be integers');
     }
   }