Fix a few code style things

This should reduce the number of warnings given by the code style check. The remaining warnings are questionable.

doc.zih.tu-dresden.de/util/check-code-style.sh

@@ -110,7 +110,7 @@ fi
 
 any_fails=false
 
-for file in $files; do
+for file in ${files}; do
   # Skip the check of this current ($0) script.
   if echo "${file}" | grep -qP "check-code-style.sh$"; then
     continue