Description:
------------
The highlight_file() and highlight_string() functions don't translate the leading space of a line to   when this line has exactly one leading space (or identation space if you prefer).

As web browsers don't display leading spaces of a line (that are not   of course), this single leading space then disapears on the output visible in the browser.

When there are two or more spaces, they are all correctly translated to   however, and the identation is visible.

Reproduce code:
---------------
highlight_string('<?php

no_leading_space($test);
 one_leading_space($test);
  two_leading_spaces($test);
   three_leading_spaces($test);
    four_leading_spaces($test);

?>');


Expected result:
----------------
<?php

no_leading_space($test);
 one_leading_space($test);
  two_leading_spaces($test);
   three_leading_spaces($test);
    four_leading_spaces($test);

?>

with HTML source (excerpt):

... <font color="#007700">);<br />&nbsp;</font><font color="#0000BB">one_leading_space</font> ...

Actual result:
--------------
<?php

no_leading_space($test);
one_leading_space($test);
  two_leading_spaces($test);
   three_leading_spaces($test);
    four_leading_spaces($test);

?>

with HTML source (excerpt):

... <font color="#007700">);<br /> </font><font color="#0000BB">one_leading_space</font> ...