#41 Check return codes everywhere

[Markus Elfring]

Some checks for return codes are missing.

Examples:
Would you like to add more error handling for return values from "strdup" like in the function "main" and from "printf" in the function "showusage"?
http://poptop.cvs.sourceforge.net/poptop/poptop/bcrelay.c?revision=1.7&view=markup