provide a default ssl_ca_path

[fschlich]

XML::Stream defaults to verifying certificates (which is good), but it fails to provide a default ssl_ca_path, which means that verification will fail with

Invalid or unreadable path specified for ssl_ca_path. at /usr/share/perl5/XML/Stream.pm line 641

unless each and every library or script using it explicitly sets such a path.

Of course it is difficult to know what path to try by default, but I'd like to suggest '/etc/ssl/certs', which should work on all Debian/Ubuntu based systems. (And if this is the wrong path on $otheros, their users will not be worse off than they are at the moment).

[KES777]

Probably the path can be filled with Mozilla::CA::SSL_ca_file() if Mozilla::CA is available.
I am not sure, but LWP do that