This commit adds code to the tapeserverd daemon to register its
drives with the vdqmd daemon.  There is a problem with the code
in that it fails to register two drives in the up state.  This
will be fixed later.

Added a constraint on MigrationJob.FileSize so that it cannot be <= 0. In particular, this makes sure that we do not try to migrate 0 size file

With this commit tapeserverd connects to the vdqm using Cgethostbyname().
It is planned to replace this use of Cgethostbyname() by getAddrInfo().

Eric found that the underlying C function getaddrinfo() is thread
safe because of RFC 3493.

The getaddrinfo() function will be used instead of the inetPton() function,
I am therefore removing inetPton() in order to reduce deadwood.

This new overloaded version still needs to be implemented.  It currently
throws an exception.

This version of connectToVdqm() is based on Cgethostbyname().  This is
a temporary implementation.  I would like that it is replaced by code
based around getaddrinfo() which is both standard and thread-safe on
linux and is therefore better than gethostbyname() whose rentrant
cousin gethostbyname_r() is a GNU extension.  According to the BSD
manual pages, the getaddrinfo() function is a replacement for and
provides more flexibility than gethostbyname().

I cannot find any information about the thread safety of getaddrinfo()
on MAC.

constraint violation errors

        Update the example configuration file of the XRootD manager node in order
        to support file checksum queries

constraint violation errors

Added explaination for a bare dynamic cast to reference, which is not to
straightforward.