git and hg diff views did not show empty context lines, a regression

from the commit(s) from issue 633. The diff parser assumed a properly
formatted diff that denotes empty context lines with a single space in
the first column. This single space however was missing, because the
hg and git backends got the diff through PHP's exec() function and
this returns already line-splitted output, but - and this is the actual
problem - removes trailing whitespace at the end of each line, essentially
making " \n" only "\n". When splitting this string now again with
PREG_SPLIT_NO_EMPTY the empty line was completely lost in the diff output.

To make it clear that an empty line does not mark a context line now, but
should stop the diff parsing, the Diff parser now also defaults to 'false'
as line type.

This commit fixes issue 688.

src/IDF/Diff.php

@@ -101,7 +101,7 @@ class IDF_Diff
                 $files[$current_file]['chunks'][] = array();
 
                 while ($i < $diffsize && ($addlines >= 0 || $dellines >= 0)) {
-                    $linetype = $this->lines[$i] != '' ? $this->lines[$i][0] : ' ';
+                    $linetype = $this->lines[$i] != '' ? $this->lines[$i][0] : false;
                     switch ($linetype) {
                         case ' ':
                             $files[$current_file]['chunks'][$current_chunk][] =