Add role="document" to modal itself

Initial fix to generalise use of modals. Generally, true role="dialog"
containers would require only forms/controls as content, with all other
text correctly and explicitly associated via
aria-labelledby/aria-describedby and similar...but as authors use modals
also as generic overlays, this extra role is required to get AT
(particularly NVDA) out of "forms" mode and reenable reading keys

docs/_includes/js/modal.html

@@ -69,7 +69,7 @@ <h3>Live demo</h3>
   <p>Toggle a modal via JavaScript by clicking the button below. It will slide down and fade in from the top of the page.</p>
   <!-- sample modal content -->
   <div id="myModal" class="modal fade" tabindex="-1" role="dialog" aria-labelledby="myModalLabel">
-    <div class="modal-dialog">
+    <div class="modal-dialog" role="document">
       <div class="modal-content">
 
         <div class="modal-header">
@@ -121,7 +121,7 @@ <h4>Overflowing text to show scroll behavior</h4>
 
 <!-- Modal -->
 <div class="modal fade" id="myModal" tabindex="-1" role="dialog" aria-labelledby="myModalLabel">
-  <div class="modal-dialog">
+  <div class="modal-dialog" role="document">
     <div class="modal-content">
       <div class="modal-header">
         <button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">&times;</span></button>
@@ -222,7 +222,7 @@ <h2 id="modals-grid-system">Using the grid system</h2>
   <p>To take advantage of the Bootstrap grid system within a modal, just nest <code>.container-fluid</code> within the <code>.modal-body</code> and then use the normal grid system classes within this container.</p>
 <!-- sample modal content -->
   <div id="gridSystemModal" class="modal fade" tabindex="-1" role="dialog" aria-labelledby="gridModalLabel">
-    <div class="modal-dialog">
+    <div class="modal-dialog" role="document">
       <div class="modal-content">
         <div class="modal-header">
           <button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">&times;</span></button>
@@ -270,7 +270,7 @@ <h4 class="modal-title" id="gridModalLabel">Modal title</h4>
 </div><!-- /example -->
 {% highlight html %}
 <div class="modal fade" role="dialog" aria-labelledby="gridSystemModalLabel">
-  <div class="modal-dialog">
+  <div class="modal-dialog" role="document">
     <div class="modal-content">
       <div class="modal-header">
         <button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">&times;</span></button>
@@ -323,7 +323,7 @@ <h2 id="modals-related-target">Varying modal content based on trigger button</h2
     ...more buttons...
 
     <div class="modal fade" id="exampleModal" tabindex="-1" role="dialog" aria-labelledby="exampleModalLabel">
-      <div class="modal-dialog">
+      <div class="modal-dialog" role="document">
         <div class="modal-content">
           <div class="modal-header">
             <button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">&times;</span></button>
@@ -356,7 +356,7 @@ <h4 class="modal-title" id="exampleModalLabel">New message</h4>
 ...more buttons...
 
 <div class="modal fade" id="exampleModal" tabindex="-1" role="dialog" aria-labelledby="exampleModalLabel">
-  <div class="modal-dialog">
+  <div class="modal-dialog" role="document">
     <div class="modal-content">
       <div class="modal-header">
         <button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">&times;</span></button>