support 'whence' arg to seek()
diff --git a/Lib/mailbox.py b/Lib/mailbox.py
index 8a54b46..e60b73b 100755
--- a/Lib/mailbox.py
+++ b/Lib/mailbox.py
@@ -12,8 +12,13 @@
 		self.fp = fp
 		self.seekp = 0
 
-	def seek(self, pos):
-		self.seekp = pos
+	def seek(self, pos, whence=0):
+		if whence==1:		# Relative to current position
+			self.pos = self.pos + pos
+		if whence==2:		# Relative to file's end
+			self.pos = self.stop + pos
+		else:			# Default - absolute position
+			self.pos = self.start + pos
 
 	def next(self):
 		while 1: