This amends commit b9a85831.

The rebuild is needed for commit d3b9aaba.

If this is set to true (default false) we assume the storage-dir is
shared, organized by realm/domain, with uses other than voicemail, so
we adopt a directory structure of:

  <storage_dir>/<realm>/voicemail/<id>

This replaces the semantics of the storage-dir parameter without the
deprecation notice.  The behavior of storage-dir never should have
been deprecated, though it was probably correct to deprecate the name
itself.

Rather than having both vm-storage-dir and vm-domain-storage-dir it
might be nice if the config system could just notice at what level it
was defined and do the right thing.  Indeed, this is why I'd left
things as-is for so long.

But as Master Foo famously said, "which one will reach the other side
of the river: the one who dreams of a raft, or the one that hitchhikes
to the next bridge?"

FS-5329

Some OSes like linux provide a mechanism for sending TCP keepalive
pings.  Sofia provides its own mechanism for doing this in userspace.
We shouldn't conflate these two mechanisms.

FS-6104

This separates out the Linux socket TCP keepalive timeout interval
from Sofia's internal mechanisms.  Earlier we tied these together.  In
retrospect this seems improper.

These two values can now be set separately.

You might, for example, want to keep the Sofia internal mechanism
disabled completely while enabling the platform-based mechanism if
your platform supports it.

We also here reform the default value of the socket TCP keepalive
parameter to 30 seconds.

This is what commit a0e9639a should
have been.

FS-6104

Sofia keeps the TCP keepalive timeout in milliseconds, but Linux
expects the value in seconds.  Before this change, it's unlikely the
TCP_KEEPIDLE and TCP_KEEPINTVL calls were having much effect as we
would have been passing them a huge value.

FS-6104

FS-6128 FS-6200 --resolve allocating the sofia_private on the nua_handle seems to lead to memory corruption, changing it back to malloc as done in the version before the regression