implementation from lib/hostip6.c to lib/curl_addrinfo.c
and prototypes from lib/hostip.h to lib/curl_addrinfo.h

Use a wrapper function to call system's getaddrinfo().

but I'm not in the mood to fight nroff right now...

curl_easy_pause() during a chunky upload. Reported by Steve Roskowski.

 and CHECK_FUNC_GETADDRINFO_UNFREEABLE_AI_CANONNAME
internal to CHECK_FUNC_GETADDRINFO

section of the code that was odd-looking previously

function returns an addrinfo with an unfreeable ai_canonname member ptr.

can be created before resolving the IPv6 name.  In the context of running
a test, it doesn't make sense to run an IPv6 test when a host is resolvable
but IPv6 isn't usable.  This should fix failures of test 1085 on hosts with
library and DNS support for IPv6 but where actual use of IPv6 has been
administratively disabled.

function returns an addrinfo with an unfreeable ai_addr member ptr.

test #559 tests internal hash create/add/destroy

when allocating/building the fake Curl_addrinfo.

now to minimally exercise some internal hash routines.

  Select ANSI C89 dialect plus GNU extensions, again.

and isn't strictly needed here.