Use class="u-monospace" for diffs

This is necessary for proper formatting of diffs. HTML for all other
monospaced blocks was already being emitted with this attribute, causing
inconsistent application of typefaces on diffs.

Bug: issue 122
Change-Id: Ic0a317c4ef925cefa564a367bb1c75024c67eb32

gitiles-servlet/src/main/java/com/google/gitiles/HtmlDiffFormatter.java

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/HtmlDiffFormatter.java b/gitiles-servlet/src/main/java/com/google/gitiles/HtmlDiffFormatter.java
index a290642..40eeb83 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/HtmlDiffFormatter.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/HtmlDiffFormatter.java
@@ -35,7 +35,7 @@
 
 /** Formats a unified format patch as UTF-8 encoded HTML. */
 final class HtmlDiffFormatter extends DiffFormatter {
-  private static final byte[] DIFF_BEGIN = "<pre class=\"u-pre Diff-unified\">".getBytes(UTF_8);
+  private static final byte[] DIFF_BEGIN = "<pre class=\"u-pre u-monospace Diff-unified\">".getBytes(UTF_8);
   private static final byte[] DIFF_END = "</pre>".getBytes(UTF_8);
 
   private static final byte[] HUNK_BEGIN = "<span class=\"Diff-hunk\">".getBytes(UTF_8);