refman: xhtml validity of the cover page
refman: switch all source files to utf8

 Putting utf8 everywhere helps the maintainance of the online refman.
 And anyway, this is the way to go. We should also chase and migrate
 the few remaining iso-latin-1 files elsewhere in the sources.
refman: avoid label names with whitespace (unsupported in html)
refman: for xhtml validity, add 'alt' attributes to img