#4768: store base64 encoded email body parts as text, not binary.

Patch and tests by Forest Bond.
diff --git a/Lib/email/encoders.py b/Lib/email/encoders.py
index 20feb02..0ea441d 100644
--- a/Lib/email/encoders.py
+++ b/Lib/email/encoders.py
@@ -29,7 +29,7 @@
     Also, add an appropriate Content-Transfer-Encoding header.
     """
     orig = msg.get_payload()
-    encdata = _bencode(orig)
+    encdata = str(_bencode(orig), 'ascii')
     msg.set_payload(encdata)
     msg['Content-Transfer-Encoding'] = 'base64'