In bug 1067, dom_rss_pop_document() freed a node with done_dom_node()
even though call_dom_node_callbacks() was still using that node. This
made call_dom_node_callbacks() read a function pointer from beyond the
end of an array and call that. Add assertions to detect out-of-range
node types, and comments to warn about the bug.
Fix warnings:
dom/stack.h:70: Warning: explicit link request to 'pop_dom_node' could not be resolved
dom/stack.h:71: Warning: explicit link request to 'pop_dom_nodes' could not be resolved
dom/stack.h:71: Warning: explicit link request to 'pop_dom_state' could not be resolved
dom/stack.h:115: Warning: explicit link request to 'done_dom_node' could not be resolved
Use @returns instead of \return in src/document/css/parser.c,
and other such things.
