base64 decoding is too aggressive

What steps will reproduce the problem?
1. Open the following example file: 
https://gist.github.com/1019783#file_zotero.xml using Python 2.7
2. Parse using feedparser.parse()
3. Attempt to decode the content[0]['value'] strings to UTF-8

What is the expected output? What do you see instead?
The second entry should be '{"name":"A Midsummer Night's Dream, "parent":false}'
Instead, a UnicodeDecodeError is thrown:
'ascii', 
'\x9d\xa9\x9e\x00\xc8\x9d\xb2\xe9\xa6z\xb3b\x82\x1bl\x0e\xb7\x9a\x9a\x96\xabz{_j
[\x1e', 0, 1, 'ordinal not in range(128)'

What version of the product are you using? On what operating system?
Version 5.0.1, OS X (10.6.7), Python 2.7


Please provide any additional information below.

Original issue reported on code.google.com by ursch...@gmail.com on 11 Jun 2011 at 5:22

Start by reproducing the report with the linked zotero.xml example on Python 2.7 and feedparser.parse(), then trace where the content[0]['value'] string is base64-decoded. Done means the second entry produces the expected JSON-like value and does not raise the reported UnicodeDecodeError.