XBEL bug 761: Distinguish between names and values of attributes.

XBEL bug 761: Distinguish between names and values of attributes.

When ELinks is parsing an XML element in from an XBEL bookmark file,
it collects the attributes of the element to the current_node->attrs
list.  Previously, struct attributes had room for one string only:
the last element of current_node->attrs was the name of the first
attribute, and it was preceded by the value of the first attribute,
the name of the second attribute, the value of the second attribute,
and so on.  However, when get_attribute_value() was looking for a
given name, it compared the values as well.  So, if you had for
example <bookmark id="href" href="http://elinks.cz/">, then
get_attribute_value("href") would incorrectly return "href".

To fix this confusion, store values in the new member
attributes.value, rather than in attributes.name.