Issue #7143: get_payload used to strip any trailing newline from a

Issue #7143: get_payload used to strip any trailing newline from a
base64 transfer-encoded payload *after* decoding it; it no longer does.
email had a special method in utils, _bdecode, specifically to do this,
so it must have served a purpose at some point, yet it is clearly wrong
per RFC.  Fixed with Barry's approval, but no backport.  Email package
minor version number is bumped, now version 4.0.1.

Patch by Joaquin Cuenca Abela.