[error prone] fix ReferenceEquality warning in CommitGraphPane#authorFor

Change-Id: I4d620ca65f7cd85863fe8b7182b01d262fbe3504
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.ui/src/org/eclipse/jgit/awtui/CommitGraphPane.java

 import org.eclipse.jgit.lib.PersonIdent;
 import org.eclipse.jgit.revplot.PlotCommit;
 import org.eclipse.jgit.revplot.PlotCommitList;
+import org.eclipse.jgit.util.References;
 
 /**
  * Draws a commit graph in a JTable.
 		}
 
 		PersonIdent authorFor(PlotCommit<SwingLane> c) {
-			if (c != lastCommit) {
+			if (!References.isSameObject(c, lastCommit)) {
 				lastCommit = c;
 				lastAuthor = c.getAuthorIdent();
 			}