PlotRefComparator: fix #timeof

The #timeof method returned
- the commit time in seconds since the epoch for RevCommits
- the tagger time in milliseconds since the epoch for annotated tags

Fix this by converting commit time to milliseconds to ensure consistent
timestamp comparison of tags and commits.

Change-Id: I91621da19c234fe823788d85e4077750cb5cba1a

org.eclipse.jgit/src/org/eclipse/jgit/revplot/PlotWalk.java

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/revplot/PlotWalk.java b/org.eclipse.jgit/src/org/eclipse/jgit/revplot/PlotWalk.java
index 39e8fd8..c8c454a 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/revplot/PlotWalk.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/revplot/PlotWalk.java
@@ -169,8 +169,9 @@ public int compare(Ref o1, Ref o2) {
 		}
 
 		long timeof(RevObject o) {
-			if (o instanceof RevCommit)
-				return ((RevCommit) o).getCommitTime();
+			if (o instanceof RevCommit) {
+				return ((RevCommit) o).getCommitTime() * 1000L;
+			}
 			if (o instanceof RevTag) {
 				RevTag tag = (RevTag) o;
 				try {