vquery_yesno():  fix silent message truncation
vquery_yesno():  fix silent message truncation

This and the similar query_tty_yesno() have a much-too-small 1k message buffer,
and silently truncate messages longer than that, including the [Y/n] prompt.

Use a 64k buffer and report truncation.

en90/pkg,khorben/pkg,khorben/pkg,khorben/pkg,en90/pkg