Dropdowns overhaul:

1. Removed broken and unused dropup examples from the navs/pills docs
2. New defaults for dropdown menus: all corners are rounded and always 1px offset from top unless otherwise specified
3. Refined active and open states for button dropdowns by adding a darker background color for each button variation when opened; also changed the opened dropdown-toggle's inset shadow to match that of an :active button
4. Generalized .dropdown.open to just .open, thus removing a few lines from button-groups.less.
5. Annnnnnnnnd I think that's it.

less/dropdowns.less

@@ -34,7 +34,7 @@
   margin-left: 2px;
 }
 .dropdown:hover .caret,
-.open.dropdown .caret {
+.open .caret {
   .opacity(100);
 }
 
@@ -49,14 +49,12 @@
   display: none; // none by default, but block on "open" of the menu
   min-width: 160px;
   padding: 4px 0;
-  margin: 0; // override default ul
+  margin: 1px 0 0; // override default ul
   list-style: none;
   background-color: @dropdownBackground;
-  border-color: #ccc;
-  border-color: rgba(0,0,0,.2);
-  border-style: solid;
-  border-width: 1px;
-  .border-radius(0 0 5px 5px);
+  border: 1px solid #ccc;
+  border: 1px solid rgba(0,0,0,.2);
+  .border-radius(5px);
   .box-shadow(0 5px 10px rgba(0,0,0,.2));
   -webkit-background-clip: padding-box;
      -moz-background-clip: padding;
@@ -99,22 +97,18 @@
 
 // Open state for the dropdown
 // ---------------------------
-.dropdown.open {
+.open {
   // IE7's z-index only goes to the nearest positioned ancestor, which would
   // make the menu appear below buttons that appeared later on the page
   *z-index: @zindexDropdown;
 
-  .dropdown-toggle {
-    color: @white;
-    background: #ccc;
-    background: rgba(0,0,0,.3);
-  }
   .dropdown-menu {
     display: block;
   }
 }
 
 // Right aligned dropdowns
+// ---------------------------
 .pull-right .dropdown-menu {
   left: auto;
   right: 0;