Add a method to SystemReader to get the time zone

Change-Id: Ifd31f408ed2c5b7869694b715fea3219e74963ef

org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/MockSystemReader.java

 
 	@Override
 	public int getTimezone(long when) {
-		return TimeZone.getTimeZone("GMT-03:30").getOffset(when) / (60 * 1000);
+		return getTimeZone().getOffset(when) / (60 * 1000);
 	}
 
+	@Override
+	public TimeZone getTimeZone() {
+		return TimeZone.getTimeZone("GMT-03:30");
+	}
 }

org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/Log.java

 import org.eclipse.jgit.notes.NoteMap;
 import org.eclipse.jgit.revwalk.RevCommit;
 import org.eclipse.jgit.revwalk.RevTree;
+import org.eclipse.jgit.util.SystemReader;
 import org.kohsuke.args4j.Option;
 
 @Command(common = true, usage = "usage_viewCommitHistory")
 class Log extends RevWalkTextBuiltin {
-	private final TimeZone myTZ = TimeZone.getDefault();
+	private final TimeZone myTZ = SystemReader.getInstance().getTimeZone();
 
 	private final DateFormat fmt;
 

org.eclipse.jgit/src/org/eclipse/jgit/util/SystemReader.java

 
 		@Override
 		public int getTimezone(long when) {
-			return TimeZone.getDefault().getOffset(when) / (60 * 1000);
+			return getTimeZone().getOffset(when) / (60 * 1000);
+		}
+
+		public TimeZone getTimeZone() {
+			return TimeZone.getDefault();
 		}
 	};
 
 	 * @return the local time zone
 	 */
 	public abstract int getTimezone(long when);
+
+	/**
+	 * @return system time zone, possibly mocked for testing
+	 */
+	public abstract TimeZone getTimeZone();
 }