* New configuration statement: IgnoreSRVWeight

Instructs pound to ignore weight value of an SRV record when
generating new backend from it.  Priority of the generated backend is
copied from its matrix backend.

* New configuration statement: OverrideTTL

When used with dynamic backends, instructs pound to use the supplied
value as TTL, instead of the one returned in DNS response.

* Load balancing code revisited

Removed arbitrary limit on backend priority value.  The allowed range
is now 1..65535.

Remove priority mapping for SRV-generated backends.  SRV weights are
assigned to backend priorities verbatim.

* Fix access to freed memory in session handling code.

* Improve testsuite

Check for missing perl modules and skip tests if needed.

DNS-based tests are disabled by default, due to their experimental
nature.  Use --enable-dns-tests to enable them.

The poundharness.pl script runs a self-test when invoked with the
--fakedns option, to avoid spurious test failures.