Remove possiblity of multiple close on same fd

With all the async connects and disconnects and error handling
going on in hiredis, we need to centralize how we close our fd
and set it so it doesn't get re-closed.  Prior to this commit,
sometimes we'd close(fd), run an async error handler, then
call close(fd) again.

To stop multiple closes, we now set fd to -1 after we free it,
but that requires not passing fd as an independent argument to
functions.

This commit moves all fd usage to c->fd.  Since the context
has a fd field and all functions receive the context, it makes
more sense to use the fd inside of c instead of passing along fd
as an independent argument.

Also, by only using c->fd, we can set c->fd after we close it to
signify we shouldn't re-close the same fd again.

This does change one semi-public interface function redisCheckSocketError()
to only take (context) instead of (context, fd).  A search on github
returned zero occasions of people using redisCheckSocketError()
outside of net.{c,h} in hiredis itself.

Commit inspired by the bug report at:
https://groups.google.com/forum/#!topic/redis-db/mQm46XkIPOY

Thanks go out to Thijs for trying high-frequency reconnects on
a host that isn't there.

Closes #230
Stop redisCheckSocketError from more than checking

redisCheckSocketError should only CheckSocketError and not
close any misbehaving sockets.  If CheckSocketError discovers
a problem, the caller will discover the contest is in ERR
and will start destroying the context (which involves
finalizing all callbacks (which may still be using
fd for something, so we should not close fd until all
callbacks have been told we are failing) and eventually
close the fd in redisFree() immediately before the
context is released).
Fix potential undefined struct read

All the assignments to cb are inside conditionals, so it's
vaguely possible it never gets initialized before we try
to read from it with (cb.fn == NULL).

Condition discovered with scan-build.

Closes #229
Add ability to bind source address on connect

Some environments require binding to specific source addresses instead
of letting the system determine which IP a connection should originate
from.

Closes #233
Add redisConnectFd() and redisFreeKeepFd()

These allows for easier integration of hiredis with external
code that wants to manage its fds, say for instance in a pool.

Closes #223
Fix "host cannot be resolved test" test

Closes #186
Libuv: Fix compile warnings and C++ compatability

Closes #189
Add new redisAppendFormatedCommand with tests

Closes #202
Define redisLibuvAttach as static

Closes #206
Define _XOPEN_SOURCE for NetBSD

This is backported from
https://github.com/antirez/redis/commit/289942b6259670fe3dcfaffdd0135c27f14c61c0
Upgrade sds to latest version

SDS is now broken out of Redis into its own project, so include
the latest version from the SDS repo.

This is a backport of the Redis commit doing the same to the bundled hiredis:
https://github.com/antirez/redis/commit/320fa02b9b48ee1c63d88db6344fc0d328e24853
Add missing license and copyright for adapters

This is a backport of
https://github.com/antirez/redis/commit/d01aad329c259a7276c448cee6696b04dfa6f8c1
Fix Makefile test to use more compatible syntax

The existing way is not compatible with a lot of shells, including most
bash installations, because the echos that generates the configuration
sent to redis-server doesn't expand the escapes. Adding '-e' to the
echo works under bash, but breaks on the Travis CI server.

This is my attempt to find an alternative that works everywhere.
[committer note: it doesn't work under Solaris make, but the Makefile
was already broken under Solaris make.  Solaris users must use gmake.]

Closes #224 and Closes #221
Fix build under Solaris

Solaris doesn't define the TCP options we try to set.  Let's
ignore those under Solaris.

Closes #207
Merge pull request #234 from mattsta/next-version

Next version of hiredis
Fix const correctness
File descriptors can be 0
Fix HIREDIS_MINOR

Closes #219.
Less surprising behaviour.

Make redisFree() and freeReplyObject() less surprising by behaving just
like free(). That is, don't crash when passing in NULL.
Add tests for redisFree() and freeReplyObject()

Test that redisFree() and freeReplyObject() do not crash when NULL is
passed in.