resolver: make new name resolutions reread /etc/resolv.conf

 if 256+ seconds passed since last read;
 fix cases where we switch to next search domain instead of switching
 to new server
 optimize ip4/ip6 combined cases;
 rewrite for(;;) loops so that it's clearer what's going on;
 document buffer usage;
 add TODOs and FIXMEs (for one, gethostbyname2 does not fill
 ->h_aliases field in the result AT ALL, and is iffy in general)

    text    data     bss     dec     hex filename
- 245898    1403   11904  259205   3f485 libuClibc-0.9.30-svn.so
+ 245785    1403   11904  259092   3f414 libuClibc-0.9.30-svn.so