Implement FileSnapshot.toString() to help debugging

Change-Id: Ic18d051327e491d5834929ff7fa28381f0f972c4
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileSnapshot.java

@@ -44,6 +44,10 @@
 package org.eclipse.jgit.internal.storage.file;
 
 import java.io.File;
+import java.text.DateFormat;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.Locale;
 
 import org.eclipse.jgit.util.FS;
 
@@ -207,6 +211,18 @@ public class FileSnapshot {
 		return (int) lastModified;
 	}
 
+	@Override
+	public String toString() {
+		if (this == DIRTY)
+			return "DIRTY"; //$NON-NLS-1$
+		if (this == MISSING_FILE)
+			return "MISSING_FILE"; //$NON-NLS-1$
+		DateFormat f = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS", //$NON-NLS-1$
+				Locale.US);
+		return "FileSnapshot[modified: " + f.format(new Date(lastModified)) //$NON-NLS-1$
+				+ ", read: " + f.format(new Date(lastRead)) + "]"; //$NON-NLS-1$ //$NON-NLS-2$
+	}
+
 	private boolean notRacyClean(final long read) {
 		// The last modified time granularity of FAT filesystems is 2 seconds.
 		// Using 2.5 seconds here provides a reasonably high assurance that