Add support for passphrase constraints options and checkpin inquiry
* pinentry/pinentry.h (struct pinentry): Add fields constraints_enforce, constraints_hint_short, constraints_hint_long, constraints_error_title. * pinentry/pinentry.h, pinentry/pinentry.c (pinentry_inq_checkpin): New. * pinentry/pinentry.c (pinentry_reset): Take care of the new fields. (do_unescape_inplace): New. (option_handler): New options "constraints-enforce", "constraints-hint-short", "constraints-hint-long", "constraints-error-title".
This implements the common pinentry side for checking whether a new
passphrase satisfies the passphrase constraints.