fix test_SeqIO_online for GI:16130152

This test fails because GI:16130152 has recently been modified so that the record returned when querying Entrez with rettype="gb" does not contain the protein sequence. This (minimal) patch calls Entrez with rettype="gbwithparts" instead of rettype="gb" so that the returned record includes the protein sequence. 

Since SeqIO does not accept "gbwithparts" as a file format specifier, I added a check to tell SeqIO.read to parse the record as a "gb" file when "gbwithparts" has been specified

biopython-dev thread: http://lists.open-bio.org/pipermail/biopython-dev/2013-May/010608.html