Completion of error handling

[elfring]

I have looked at a few source files for your current software. I have noticed that some checks for return codes are missing.

Would you like to add more error handling for return values from functions like the following?

• strdup ⇒ parse_argv
• fprintf ⇒ check_uniqueness

[telmich]

I am open for pull requests that make the code more clean or robust, so the answer is yes :-)

[elfring]

Are you interested to apply aspect-oriented software development? How do you think about to encapsulate error detection and corresponding exception handling as a reusable aspect in your software?