cmake: enable IPv6 by default if available

ENABLE_IPV6 depends on HAVE_GETADDRINFO or you will get a
Curl_getaddrinfo_ex error. Enable IPv6 by default, disabling it if
struct sockaddr_in6 is not found in netinet/in.h.

Note that HAVE_GETADDRINFO_THREADSAFE is still not set as it needs more
platform checks even though POSIX requires a thread-safe getaddrinfo.

Verified on Arch Linux x86_64 with glibc 2.20-2 and Linux 3.16-rc7.

Signed-off-by: Peter Wu <peter@lekensteyn.nl>
tests: move TESTCASES to Makefile.inc, add show for cmake

This change allows runtests.pl to be run from the CMake builddir:

    export srcdir=/tmp/curl/tests;
    perl -I$srcdir $srcdir/runtests.pl -l

In order to make this possible, all test cases have been moved from
Makefile.am to Makefile.inc.

Signed-off-by: Peter Wu <peter@lekensteyn.nl>
vtls/*: deprecate have_curlssl_md5sum and set-up default md5sum implementation
gskit: supply dummy randomization function
vtls: remove QsoSSL
Factorize pinned public key code into generic file handling and backend specific
pinning: minor code style policing
singleipconnect: remove dead assignment never used

cppcheck pointed this out.
cleanups: reduce variable scope

cppcheck pointed these out.
CURLOPT_TLSAUTH_*.3: fix reference typos