Add perlbug -p option for attaching patches.

Log files and other text attachments should also be fine as long
as they aren't big enough to be rejected by RT.

Only text attachments are supported, as other kinds would involve
wrestling with myriad MIME types and possibly content transfer
encodings.  This should be fine for binary patches, though, as
git format-patch encodes those in Base85, so the patch file itself
is still text.
Switch perlbug mail sender on VMS.

The VMS mail utility can't do attachments because it always adds
a blank line in front of any headers you add.  So use the Send
From File utility, which has been documented and supported for
any release in the last decade and was latently present before
that.

It takes the whole message verbatim just like sendmail, but also
needs the envelope prepended.
Make perlbug Unicode-aware.

Try to do input in whatever the locale wants and output raw in
hopes that will best survive mail transport.

Except when reading in a patch file, we'll also use raw for input
because there may be multiple encodings in the patch, and we'll
also use raw for input when reading in the report file that we've
written out raw.

We attempt to detect the locale encoding using the private and
undocumented _get_locale_encoding() function of the deprecated
encoding pragma module.  But it's what the open pragma does and
we protect ourselves by checking that it's available and falling
back to an empty layer specification ("<:") if we can't load that
function.  That should also give us something workable when there
is no dynamic loading, such as under miniperl.
perldelta for perlbug changes.