Do not call chown(2) unless we need to Apparently some glibc/kernel combinations will fail for unprivileged users even for chown(-1, -1). Fixes the FTBFS on sparc64.
Fix optstring in unixserver.c Both manual page and getopt loop mention '-d' and '-D' command line option, but letters 'd' and 'D' was missing from getopt string, causing `unixserver' to consider `-d' and `-D' options invalid.
Catch overflow errors when converting strings to numbers Passing e.g. `-u 99999999999` would not change the variable at all, yet not be reported as an error.
