Add a fixed: option to bootstrap.popover and use it

(imported from commit fe8768b8a320df7670c204880bffb3932568cc5e)

zephyr/static/third/bootstrap/js/bootstrap.js

@@ -1221,6 +1221,7 @@
         , actualHeight
         , placement
         , tp
+        , newtop
 
       if (this.hasContent() && this.enabled) {
         $tip = this.tip()
@@ -1261,6 +1262,14 @@
             break
         }
 
+        if (this.options.fixed) {
+          // If using position: fixed, position relative to top of
+          // viewport
+          newtop = tp.top - $(document).scrollTop()
+          tp = $.extend(tp, {top: newtop,
+                             position: 'fixed'})
+        }
+
         $tip
           .css(tp)
           .addClass(placement)
@@ -1388,6 +1397,7 @@
   , title: ''
   , delay: 0
   , html: true
+  , fixed: false
   }
 
 }(window.jQuery);