Blame parent instead of self if blame link would go nowhere

This is intended to make walking back through history on a file
easier.

Bug: Issue 64
Change-Id: I2f8540021d8d59cd69f9b4e2088b607d40086216

gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameServlet.java

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameServlet.java b/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameServlet.java
index 7f18de2..9c5edbd 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameServlet.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameServlet.java
@@ -219,10 +219,17 @@
         }
         Map<String, Object> e = Maps.newHashMapWithExpectedSize(6);
         e.put("abbrevSha", abbrevSha);
+        String blameParent = "";
+        String blameText = "blame";
+        if (view.getRevision().getName().equals(r.getSourceCommit().name())) {
+          blameParent = "^";
+          blameText = "blame^";
+        }
         e.put("blameUrl", GitilesView.blame().copyFrom(view)
-            .setRevision(r.getSourceCommit().name())
+            .setRevision(r.getSourceCommit().name() + blameParent)
             .setPathPart(r.getSourcePath())
             .toUrl());
+        e.put("blameText", blameText);
         e.put("commitUrl", GitilesView.revision().copyFrom(view)
             .setRevision(r.getSourceCommit().name())
             .toUrl());

gitiles-servlet/src/main/resources/com/google/gitiles/templates/BlameDetail.soy

diff --git a/gitiles-servlet/src/main/resources/com/google/gitiles/templates/BlameDetail.soy b/gitiles-servlet/src/main/resources/com/google/gitiles/templates/BlameDetail.soy
index a35b6e2..f5110d8 100644
--- a/gitiles-servlet/src/main/resources/com/google/gitiles/templates/BlameDetail.soy
+++ b/gitiles-servlet/src/main/resources/com/google/gitiles/templates/BlameDetail.soy
@@ -55,7 +55,7 @@
           <td class="Blame-time">{$region.author.time}</span>
           <td class="Blame-regionLink">
             [<a href="{$region.diffUrl}">{msg desc="text for diff URL"}diff{/msg}</a>]
-            [<a href="{$region.blameUrl}">{msg desc="text for blame URL"}blame{/msg}</a>]
+            [<a href="{$region.blameUrl}">{msg desc="text for blame URL"}{$region.blameText}{/msg}</a>]
           </td>
         {else}
           <td colspan="4"></td>