Ensured that the Mallard snippets also activate XML snippets.
Corrected the areaset snippet.
Corrected the coref snippet.
Adjusted the entry snippet.
Added the id attribute to the procedure and task snipptes.
Enhanced the XML snippets.
Added the id attribute to the refsectX and refsection snippets.
Added DocBook 4.5 snippets for the UltiSnips plug-in.