Mediawiki parser crashes on unquoted table attribute values

[lmichelbacher]

Unquoted attribute values in table headers throw off the parser:

pandoc:
Error at "source" (line 835, column 42):
unexpected "2"
expecting "\""
{| cellpadding=“3” cellspacing=“0" width=250 align="right" rules="all" style="margin: 1em; background: #ffffff; border: 2px solid #aaa; font-size: 100%;"
                                         ^

Some work has been done to make table parsing more robust but this one is still an issue.