Fix for ScanProsite.read, works with Python 2 and 3

ScanProsite.read fails on Python 3, this fix is backwards compatible
with Python 2.

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Which operating system and hardware (32 bit or 64 bit) you are using:
Linux 3.9.4-1-ARCH #1 SMP PREEMPT Sat May 25 16:14:55 CEST 2013 x86_64 GNU/Linux

Python version:
Python 3.3.2 / Python 2.7.5

Biopython version
1.61

Traceback that occurs (the full error message):
Traceback (most recent call last):
  File "prst.py", line 14, in <module>
    result = ScanProsite.read(handle)
  File "/usr/lib/python3.3/site-packages/Bio/ExPASy/ScanProsite.py", line 54, in read
    saxparser.parse(handle)
  File "/usr/lib/python3.3/xml/sax/expatreader.py", line 107, in parse
    xmlreader.IncrementalParser.parse(self, source)
  File "/usr/lib/python3.3/xml/sax/xmlreader.py", line 123, in parse
    self.feed(buffer)
  File "/usr/lib/python3.3/site-packages/Bio/ExPASy/ScanProsite.py", line 75, in feed
    raise ValueError(data)
ValueError: b'<?xml version="1.0" encoding="UTF-8"?>\n<matchset xmlns="urn:expasy:scanprosite" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="urn:expasy:scanprosite http://expasy.org/tools/scanprosite/scanprosite.xsd" n_match="3" n_seq="1">\n  <match>\n    <sequence_ac>USERSEQ1</sequence_ac> <start>428</start> <stop>436</stop> <signature_ac>PS00197</signature_ac> <level_tag>(-1)</level_tag>\n  </match>\n  <match>\n    <sequence_ac>USERSEQ1</sequence_ac> <start>452</start> <stop>463</stop> <signature_ac>PS00022</signature_ac> <level_tag>(-1)</level_tag>\n  </match>\n  <match>\n    <sequence_ac>USERSEQ1</sequence_ac> <start>463</start> <stop>471</stop> <signature_ac>PS00197</signature_ac> <level_tag>(-1)</level_tag>\n  </match>\n\n</matchset>\n'

Example code that breaks:
https://github.com/luizirber/rosalind/blob/master/prst.py

A data file that causes the problem:
The sample dataset from http://rosalind.info/problems/prst/ can be used, but any valid search with ScanProsite will trigger the error.