hgweb: file diff and changesets views behave like file source view This gives all the benefits introduced before for file source view, namely code selection without line numbers and correct indents, highlighting line which is linked to, long lines wrapping. Implementation strategy is also the same as for file source view: all the lines are put in a sigle pre tag with span's for each line. Correct line numbering (same as before this patch) is achieved with nested CSS counters.