fixes #4458: improve support for .btn + .btn in .btn-groups and .btn-toolbars

docs/assets/css/bootstrap.css

@@ -3334,6 +3334,7 @@ input[type="submit"].btn.btn-mini {
   *zoom: 1;
 }
 
+.btn-toolbar .btn + .btn,
 .btn-toolbar .btn-group + .btn,
 .btn-toolbar .btn + .btn-group {
   margin-left: 5px;
@@ -3341,12 +3342,15 @@ input[type="submit"].btn.btn-mini {
 
 .btn-group > .btn {
   position: relative;
-  margin-left: -1px;
   -webkit-border-radius: 0;
      -moz-border-radius: 0;
           border-radius: 0;
 }
 
+.btn-group > .btn + .btn {
+  margin-left: -1px;
+}
+
 .btn-group > .btn,
 .btn-group > .dropdown-menu {
   font-size: 14px;
@@ -3516,7 +3520,6 @@ input[type="submit"].btn.btn-mini {
   display: block;
   float: none;
   width: 100%;
-  margin-left: 0;
   -webkit-border-radius: 0;
      -moz-border-radius: 0;
           border-radius: 0;
@@ -3524,6 +3527,7 @@ input[type="submit"].btn.btn-mini {
 
 .btn-group-vertical .btn + .btn {
   margin-top: -1px;
+  margin-left: 0;
 }
 
 .btn-group-vertical .btn:first-child {

less/button-groups.less

@@ -25,6 +25,7 @@
     display: inline-block;
     .ie7-inline-block();
   }
+  .btn + .btn,
   .btn-group + .btn,
   .btn + .btn-group {
     margin-left: 5px;
@@ -34,9 +35,11 @@
 // Float them, remove border radius, then re-add to first and last elements
 .btn-group > .btn {
   position: relative;
-  margin-left: -1px;
   .border-radius(0);
 }
+.btn-group > .btn + .btn {
+  margin-left: -1px;
+}
 .btn-group > .btn,
 .btn-group > .dropdown-menu {
   font-size: @baseFontSize; // redeclare as part 2 of font-size inline-block hack
@@ -215,11 +218,11 @@
 .btn-group-vertical .btn {
   display: block;
   float: none;
-  margin-left: 0;
   width: 100%;
   .border-radius(0);
 }
 .btn-group-vertical .btn + .btn {
+  margin-left: 0;
   margin-top: -1px;
 }
 .btn-group-vertical .btn:first-child {