Item 'links' in sidebar is enabled when a document is reloaded with links.

In function ev_sidebar_document_changed_cb there is a test of whether
the sidebar functionalities are supported by the document. They were disabled
if the document did not support but were not enabled otherwise. To fix that, a
call to gtk_widget_set_sensitive(item, TRUE) was added to the case where 'item'
is supported by the new document.
This fixes the bug: https://bugzilla.gnome.org/show_bug.cgi?id=628617

When testing this, I realized that there was another problem. Suppose a document
with links is loaded and the 'links' page is selected in the sidebar. If I recompile
this document and remove the links, evince correctly reloads it, disables 'links' in
the sidebar, but the link page is still shown with the links in the previous document.
In order to fix this, I had to change the calls to setup_sidebar_from_metadata().

There is now a call to this function in ev_window_document_changed_cb. To avoid
duplicate calls, it was removed from setup_document_from_metadata and a separate call
to setup_sidebar_from_metadata is done in ev_window_open_document.
In the case described, setup_sidebar_from_metadata would call ev_window_sidebar_set_current_page
with 'links', even when the document did not support links (I could not find out why this
was the case. The metadata remains the same? Should it?). Originally the method would not
change the current page of the sidebar, but now a default case was added so that
'thumbnails' is selected if everything else fails.
Debug printing for search of ordinals. Report to poppler.
Commenting out the debug printing.