Fixup auto-expand

* Fix a css bug preventing bottom bar from sticking to the bottom.
* Resize discussion container as a function of the overall window
  height. The previous difference-based method gives the wrong result
  when the window height changes but the bottom-bar height stays the
  same.

// FREEBIE

js/views/conversation_view.js

@@ -213,14 +213,12 @@
             }
 
             var $discussionContainer = this.$('.discussion-container'),
-                $discussionContainerPrevHeight = $discussionContainer.outerHeight(),
+                $bottomBar = this.$('.bottom-bar');
-                $bottomBar = this.$('.bottom-bar'),
-                $bottomBarPrevHeight = $bottomBar.outerHeight();
 
             window.autosize(this.$messageField);
             $bottomBar.outerHeight(this.$messageField.outerHeight() + 1);
             var $bottomBarNewHeight = $bottomBar.outerHeight();
-            $discussionContainer.outerHeight($discussionContainerPrevHeight - ($bottomBarNewHeight - $bottomBarPrevHeight));
+            $discussionContainer.outerHeight(this.$el.outerHeight() - $bottomBarNewHeight - this.$('#header').outerHeight());
         },
 
         forceUpdateMessageFieldSize: function (event) {

stylesheets/_conversation.scss

@@ -320,7 +320,7 @@
   $button-width: 36px;
 
   position: fixed;
-  bottom: 1; // offset 1 for window frame.
+  bottom: 1px; // offset 1 for window frame.
   height: 36px;
   width: calc(100% - 2px);
   border-top: 1px solid $grey_l;

stylesheets/manifest.css

@@ -661,7 +661,7 @@ input.search {
 
 .bottom-bar {
   position: fixed;
-  bottom: 1;
+  bottom: 1px;
   height: 36px;
   width: calc(100% - 2px);
   border-top: 1px solid #f3f3f3;