Give the variablelist a margin.

[SVN r51804]

doc/html/boostbook.css

@@ -304,6 +304,11 @@
     Variable Lists
 =============================================================================*/
 
+    div.variablelist
+    {
+        margin: 1em 0;
+    }
+
     /* Make the terms in definition lists bold */
     div.variablelist dl dt,
     span.term

doc/src/boostbook.css

@@ -304,6 +304,11 @@
     Variable Lists
 =============================================================================*/
 
+    div.variablelist
+    {
+        margin: 1em 0;
+    }
+
     /* Make the terms in definition lists bold */
     div.variablelist dl dt,
     span.term