[2.7] bpo-13407: Mention that bz2/tarfile doesn't support multi-stream bzip2 files (GH-8428)

* bpo-13407: Mention that tarfile doesn't support multistream bzip2 files

* Add mention to bz2 module also

Author: andresdelfino

Doc/library/bz2.rst

@@ -35,6 +35,10 @@ Here is a summary of the features offered by the bz2 module:
 
 * Thread safety uses individual locking mechanism.
 
+.. note::
+   Handling of multi-stream bzip2 files is not supported.  Modules such as
+   `bz2file <https://github.com/nvawda/bz2file>`_ let you overcome this.
+
 
 (De)compression of files
 ------------------------

Doc/library/tarfile.rst

@@ -37,6 +37,10 @@ Some facts and figures:
   character devices and block devices and is able to acquire and restore file
   information like timestamp, access permissions and owner.
 
+.. note::
+   Handling of multi-stream bzip2 files is not supported.  Modules such as
+   `bz2file <https://github.com/nvawda/bz2file>`_ let you overcome this.
+
 
 .. function:: open(name=None, mode='r', fileobj=None, bufsize=10240, \*\*kwargs)
 

Misc/NEWS.d/next/Documentation/2018-09-29-13-40-06.bpo-13407.BRI-_D.rst

@@ -0,0 +1,2 @@
+Add a note to :mod:`bz2` and :mod:`tarfile` stating that handling of
+multi-stream bzip2 files is not supported.