fix compiler warning: external declaration in primary source file

- Andreas Schuldei improved Phil Blundell's patch for IPv6 using c-ares, and I
edited it slightly. Now you should be able to use IPv6 addresses fine even
with libcurl built to use c-ares.

Woops, partly revert my previous commit and do it slightly differently instead.
The signalling of that a global DNS cache is wanted is done by setting the
option but the setting of the intern

Woops, partly revert my previous commit and do it slightly differently instead.
The signalling of that a global DNS cache is wanted is done by setting the
option but the setting of the internal variable that it is in use must not be
done until it finally actually gets used!

NOTE and WARNING: I noticed that you can't actually switch off the global dns
cache with CURLOPT_DNS_USE_GLOBAL_CACHE but you couldn't do that previously
either and the option is very clearly and loudly documented as DO NOTE USE so
I won't bother to fix this bug now.

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I made the torture test on test 530 go through. This was actually due to
silly code left from when we switched to let the multi handle "hold" the dns
cache when using the multi interface... O

I made the torture test on test 530 go through. This was actually due to
silly code left from when we switched to let the multi handle "hold" the dns
cache when using the multi interface... Of course this only triggered when a
certain function call returned error at the correct moment.

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Adapted the c-ares code to the API change c-ares 1.5.0 brings in the
notifier callback(s).

minor patches to enable building for NetWare CLIB.
sent by Dmitry Mityugov.

Compilation fix

Major overhaul introducing http pipelining support and shared connection
cache within the multi handle.

moved ugly NetWare hack to hostip.h so that hostip.c uses it too.

Ares needs CURLRES_ADDRINFO_COPY. Curl_hostent_relocate() is gone.

Constify arguments to Curl_he2ai() and Curl_addrinfo_copy().

Constify 'hostname' and 'service' to various resolver functions.

Change the ai_addrlen type of struct addrinfo from size_t to socklen_t, per RFC 3493.

Test HAVE_GETNAMEINFO definition before using GETNAMEINFO_XXX definitions.

Fix compiler warning.

added docs and removed proto

First curl_multi_socket() commit. Should primarily be considered as an internal
code rearrange to fit the future better.

Lots of work and analysis by "xbx___" in bug #1431750
(http://curl.haxx.se/bug/view.cgi?id=1431750) helped me identify and fix two
different but related bugs:

1) Removing an easy han

Lots of work and analysis by "xbx___" in bug #1431750
(http://curl.haxx.se/bug/view.cgi?id=1431750) helped me identify and fix two
different but related bugs:

1) Removing an easy handle from a multi handle before the transfer is done
could leave a connection in the connection cache for that handle that is
in a state that isn't suitable for re-use. A subsequent re-use could then
read from a NULL pointer and segfault.

2) When an easy handle was removed from the multi handle, there could be an
outstanding c-ares DNS name resolve request. When the response arrived,
it caused havoc since the connection struct it "belonged" to could've
been freed already.

Now Curl_done() is called when an easy handle is removed from a multi handle
pre-maturely (that is, before the transfer was complteted). Curl_done() also
makes sure to cancel all (if any) outstanding c-ares requests.

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Undo last changes

Fix compiler warning and compatibility issue with the type of the parameter used in getnameinfo() to receive the length of the sockaddr struct.

kill warnings

hostthre.c: destroy_thread_data() made public. Called
from url.c: Curl_disconnect().

FTP code turned into state machine. Not completely yet, but a good start.
The tag 'before_ftp_statemachine' was set just before this commit in case
of future need.

Curl_addrinfo?_callback() and addrinfo_callback() now returns
CURLE_OK or CURLE_OUT_OF_MEMORY.
Add typecast in hostares.c.

Use plain structs and not typedef'ed ones in the hash and linked-list code.