fix tab width jittering when switching tabs

plugins/c9.ide.ace/ace.js

@@ -1823,7 +1823,7 @@ define(function(require, exports, module) {
                 container.style.position = "absolute";
                 container.style.left = "0px";
                 container.style.right = "0px";
-                container.style.top = ui.getStyle(e.htmlNode, "paddingTop");
+                container.style.top = "7px";
                 container.style.bottom = "0px";
         
                 // Create Ace editor instance

plugins/c9.ide.layout.classic/less/editor_tab.less

@@ -191,7 +191,7 @@
     height      : @pane-button-height + 3;
     z-index     : 10;
     margin-top  : -1px;
-    min-width   : 100px;
+    min-width   : 97px;
 }
 body>.session_btn.curbtn{
     cursor : default;
@@ -264,9 +264,7 @@ body>.session_btn.curbtn{
 }
 .session_btn.curbtn .sessiontab_title {
     color : @pane-button-active-color;
-    margin-top : -1px;
     text-shadow : none;
-    border-bottom: 1px dotted transparent;
 }
 .dark.session_btn.curbtn .sessiontab_title {
     color : rgba(255,255,255,0.85);