message: Highlight 2+ spaces in the middle of string too
  highlighting not only leading or trailing whitespace, but unusual
  whitespace in the middle of the string too: if there's more than one
  subsequent whitespace, highlight it to draw attention to the fact.
diff: @@ -66,8 +66,23 @@ public:
  }
  }
  + int blank_block_pos = -1;
  +
  for (auto i = s.begin(); i != s.end(); ++i)
  {
  + if (u_isblank(*i))
  + {
  + if (blank_block_pos == -1)
  + blank_block_pos = int(i - s.begin());
  + }
  + else if (blank_block_pos != -1)
  + {
  + int endpos = int(i - s.begin());
  + if (endpos - blank_block_pos >= 2)
  + highlight(blank_block_pos, endpos, LeadingWhitespace);
  + blank_block_pos = -1;
  + }
  +
  if (*i == '\\')
  {
  int pos = int(i - s.begin());
  