Import ximenia (last was tabebuia)

- BUGFIX: Fix race condition in openpam_ttyconv(3) when used with
expect scripts.

- BUGFIX: In openpam_set_option(3), when removing an option, properly
decrement the option count.

- BUGFIX: In openpam_subst(3), avoid incrementing past the end of the
template.

branches: 1.1.1.1.2;
OpenPAM Resedacea 2017-04-30

- BUGFIX: Reinstore the NULL check in pam_end(3) which was removed in
OpenPAM Radula, as it breaks common error-handling constructs.

- BUGFIX: Return PAM_SYMBOL_ERR instead of PAM_SYSTEM_ERR from the
dispatcher when the required service function could not be found.

- ENHANCE: Introduce the PAM_BAD_HANDLE error code for when pamh is
NULL in API functions that have a NULL check.

- ENHANCE: Introduce the PAM_BAD_ITEM, PAM_BAD_FEATURE and
PAM_BAD_CONSTANT error codes for situations where we previously
incorrectly used PAM_SYMBOL_ERR to denote that an invalid constant
had been passed to an API function.

- ENHANCE: Improve the RETURN VALUES section in API man pages,
especially for functions that cannot fail, which were incorrectly
documented as returning -1 on failure.