fixed: use the --porcelain option when parsing git status

the formatting for the standard git status output is unstable,
and has changed in newer versions of the git client. this lead
to missing lines in untracked files.

tests/update_reference_data.sh

@@ -262,7 +262,7 @@ then
 fi
 
 # Add potential new files
-untracked=`git status | sed '1,/Untracked files/d' | tail -n +3 | head -n -2`
+untracked=`git status --porcelain | awk '$1~/\?/{print $2}'`
 if [ -n "$untracked" ]
 then
   git add $untracked