Perl "split" can capture and group in the regexp itself,
so rely on that to shorten our code.
Comparing the /T/ HTML output of a thread from hell (on LKML with
1356 messages) reveals no difference in the rendered result.
Only the HTML source differs in newline placement before/after
the closing </span>
This allows a minor speedup on my X32 Thinkpad @ 1.6GHz with
the aforementioned LKML thread from hell: