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/navbar.less

@@ -262,8 +262,6 @@
 
 // Menu position and menu carets
 .navbar .dropdown-menu {
-  margin-top: 1px;
-  .border-radius(4px);
   &:before {
     content: '';
     display: inline-block;
@@ -304,7 +302,7 @@
 }
 // Dropdown toggle caret
 .navbar .nav .dropdown-toggle .caret,
-.navbar .nav .open.dropdown .caret {
+.navbar .nav .open .caret {
   border-top-color: @white;
   border-bottom-color: @white;
 }