fixes #4729: only use margin-top on .help-block when it follows an input, select, textarea

docs/assets/css/bootstrap.css

@@ -1792,10 +1792,15 @@ legend + .control-group {
 }
 
 .form-horizontal .help-block {
-  margin-top: 10px;
   margin-bottom: 0;
 }
 
+.form-horizontal input + .help-block,
+.form-horizontal select + .help-block,
+.form-horizontal textarea + .help-block {
+  margin-top: 10px;
+}
+
 .form-horizontal .form-actions {
   padding-left: 160px;
 }

less/forms.less

@@ -633,9 +633,16 @@ legend + .control-group {
   }
   // Remove bottom margin on block level help text since that's accounted for on .control-group
   .help-block {
-    margin-top: @baseLineHeight / 2;
     margin-bottom: 0;
   }
+  // And apply it only to .help-block instances that follow a form control
+  input,
+  select,
+  textarea {
+    + .help-block {
+      margin-top: @baseLineHeight / 2;
+    }
+  }
   // Move over buttons in .form-actions to align with .controls
   .form-actions {
     padding-left: 160px;