Also update BUILD.txt

The leak checking code which is used by the resolve and failover tests
frees talloc's autofree context which is not recommended. As a
consequence the initialization of tevent failed when it was called by
the second test and CF_FORK=no, because it holds some data in the
autofree context.

This patch introduces a global talloc context which should be uses by
the test as the root of their memory hierarchy instead of NULL. This
global context is used in the leak checking routines.

Not all types of memory leaks can be detected by the new version , it is
recommended to use valgrind or similar tools additionally.

We will allow 5s per DNS server, no retries.

* Rename structure accordingly to ares upstream
* Use new ares parsing functions in the wrappers
* fix tests for ares 1.7

If you want to turn verbosity back on, just set the environment
variable CK_VERBOSITY=verbose

* The resolv test case can now test for TXT and SRV resolving by
  specifying -t host and -s host respectively. The -n flag must still be
  passed in to enable network tests.
* Added test for the little complicated resolv_copy_hostent() function.
* Leak checking using the new tests common functions.
* Fix indentation for test_internet, since the whole function was
  modified to be able to handle SRV and TXT replies.
* Initialize the debug variable in main().

Also removed one unused variable in krb5_utils-tests.c

Add some basic unit tests of the async resolver module.
One of the tests resolves a name on the Internet, therefore it is
off by default and is turned on with the -n switch.