'net' module: tests and fixes

So far this updates #308 with a very basic test suite, and fixes IPv4 and/or IPv6 address detection.
Looks like probably the same thing, since it's logging an exit status and doesn't keep going up to the "normal" 112 tests. I'll have to look into the 'ttt' thing, unless you've patched ttt it will have trouble regardless. (So maybe that's related? Right now my theory was something to do with event firing or something, but perhaps tinytap doesn't implement t.pass/t.fail right too but masks the problem differently?) Will have to look into tomorrow…