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: 1.1.1.1.4;
OpenPAM Tabebuia 2019-02-24

- BUGFIX: Fix off-by-one bug in pam_getenv(3) which was introduced in
OpenPAM Radula.

- ENHANCE: Add unit tests for pam_{get,put,set}env(3).