without this while compiling:
```
ltree_op.c: In function ‘ltreeparentsel’:
ltree_op.c:647:4: warning: implicit declaration of function ‘GETSTRUCT’ [-Wimplicit-function-declaration]
    nullfrac = ((Form_pg_statistic) GETSTRUCT(vardata.statsTuple))->stanullfrac;
    ^
ltree_op.c:647:16: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
    nullfrac = ((Form_pg_statistic) GETSTRUCT(vardata.statsTuple))->stanullfrac;
                ^
```

which leads to:

```
roa@roabook ~PROG/postgres/ltree (pg_93*) $ createdb test
roa@roabook ~PROG/postgres/ltree (pg_93*) $ psql -U postgres test
Timing is on.
psql (9.3.2)
Type "help" for help.

test=# create extension ltree;
ERROR:  could not load library "/usr/lib64/postgresql-9.3/lib64/ltree.so": /usr/lib64/postgresql-9.3/lib64/ltree.so: undefined symbol: GETSTRUCT
Time: 3.972 ms
```