Correctly detect bzip2 compressed streams with blocksizes other than 900k.
diff --git a/Lib/tarfile.py b/Lib/tarfile.py
index 6828eab..ed5bcf2 100644
--- a/Lib/tarfile.py
+++ b/Lib/tarfile.py
@@ -627,7 +627,7 @@
     def getcomptype(self):
         if self.buf.startswith("\037\213\010"):
             return "gz"
-        if self.buf.startswith("BZh91"):
+        if self.buf[0:3] == "BZh" and self.buf[4:10] == "1AY&SY":
             return "bz2"
         return "tar"