[Devel] complete error handling

[SF Markus Elfring]

Hello,

I have noticed that unchecked function calls exist in the current source files.

Examples:
- close
- fclose
- fprintf
- fscanf
- unlink

How do you think about the open issues from the bug report "Check return codes everywhere"? Which approach do you prefer for a fix?
https://sourceforge.net/tracker/?func=detail&atid=743020&aid=1682036&group_id=139143

Regards,
Markus