ptsname: Avoid test failure on OSF/1 5.1.

ptsname: Avoid test failure on OSF/1 5.1.

* modules/ptsname-tests (Depends-on): Add 'same-inode'.
* tests/test-ptsname.c: Include <sys/stat.h>, same-inode.h.
(same_slave): New function.
(main): Use it to compare ptsname's result with the expected file name.