Drop h and hh length modifiers from printf format strings.

C already guarantees that chars and shorts get passed as int. The few uses in tinc are mainly
to print fields of struct addrinfo, and fields like ai_family have different sizes on different
platforms, which actually caused some warnings to be generated.
Fix a bug that could prevent tinc from starting correctly on Windows.
FIx the autoconf checks for res_init().
Remove the warnings when IP_DONTFRAGMENT/IPV6-DONTFRAG is not supported.

There is nothing we can do about it, and tinc will run fine anyway.