greenio: relative seek() typo _get_readahead_len; Thanks to AlanP

https://bitbucket.org/which_linden/eventlet/issue/112

eventlet/greenio.py

@@ -473,7 +473,7 @@ class GreenPipe(_fileobject):
         if whence == 1 and offset == 0: # tell synonym
             return self.tell()
         if whence == 1: # adjust offset by what is read ahead
-            offset -= self.get_readahead_len()
+            offset -= self._get_readahead_len()
         try:
             rv = os.lseek(self.fileno(), offset, whence)
         except OSError, e:

tests/greenio_test.py

@@ -627,6 +627,8 @@ class TestGreenPipe(LimitedTestCase):
         self.assertEquals(f.tell(), 2)
         f.seek(0, 1)
         self.assertEqual(f.readline(), '34567890')
+        f.seek(-5, 1)
+        self.assertEqual(f.readline(), '67890')
         f.seek(0)
         self.assertEqual(f.readline(), '1234567890')
         f.seek(0, 2)