Move `hr` to scaffolding.less (out of type.less) and simplify styles

docs/assets/css/bootstrap.css

@@ -342,6 +342,13 @@ img {
   border-radius: 500px;
 }
 
+hr {
+  margin-top: 20px;
+  margin-bottom: 20px;
+  border: 0;
+  border-top: 1px solid #eeeeee;
+}
+
 p {
   margin: 0 0 10px;
 }
@@ -590,14 +597,6 @@ dd {
   clear: both;
 }
 
-hr {
-  margin: 20px 0;
-  border: 0;
-  border-top: 1px solid #eeeeee;
-  border-bottom: 1px solid #fff;
-  border-bottom: 1px solid rgba(255, 255, 255, 0.5);
-}
-
 abbr[title],
 abbr[data-original-title] {
   cursor: help;

less/scaffolding.less

@@ -81,3 +81,15 @@ img {
 .img-circle {
   border-radius: 500px; // crank the border-radius so it works with most reasonably sized images
 }
+
+
+// Horizontal rules
+// -------------------------
+
+hr {
+  margin-top:    @line-height-computed;
+  margin-bottom: @line-height-computed;
+  border: 0;
+  border-top: 1px solid @hr-border;
+}
+

less/type.less

@@ -164,15 +164,6 @@ dd {
 // MISC
 // ----
 
-// Horizontal rules
-hr {
-  margin: @line-height-computed 0;
-  border: 0;
-  border-top: 1px solid @hr-border;
-  border-bottom: 1px solid #fff;
-  border-bottom: 1px solid rgba(255,255,255,.5);
-}
-
 // Abbreviations and acronyms
 abbr[title],
 // Added data-* attribute to help out our tooltip plugin, per https://github.com/twitter/bootstrap/issues/5257