PR fortran/15234
* io/io.h (unit_t): Rename to ...
(gfc_unit) ... this.
(unit_root, current_unit, find_file, find_unit, get_unit): Now
of type gfc_unit.
(delete_file, insert_unit, close_unit): Argument now of type
gfc_unit.
* backspace.c (st_backspace), close.c (st_close), endfile.c
(st_endfile), inquire.c (inquire_via_unit, st_inquire), open.c
(test_endfile, edit_modes, new_unit, already_open, st_open),
rewind.c (st_rewind), transfer.c (current_unit), unit.c
(internal_unit, unit_cache, rotate_left, rotate_right, insert,
insert_unit, delete_root, delete_treap, delete_unit, find_unit,
get_unit, init_units, close_unit), unix.c (find_file0,
find_file, delete_file): Replace all occurences of unit_t by
gfc_unit.

From-SVN: r81903