lbound1 default in buildint2vector/buildoidvector

Hello,

I noticed buildint2vector / buildoidvector assigns lbound1=0 as default
value, but array type shall have lbound1=1 in the default.
Is there some reasons for the difference?

When I made a simple C-function that returns result of int2vector which
carries attribute numbers of the argument.

postgres=# select attnums_of('t0','{aid,cid,bid}');
  attnums_of
---------------
 [0:2]={3,5,4}
(1 row)

Once it assigns lbound1=1 manually,

postgres=# select attnums_of('t0','{aid,cid,bid}');
 attnums_of
------------
 {3,5,4}
(1 row)

Maybe, the later one is natural.
Of course, these APIs are mostly internal, so lbound1 setting is not
significant so much.

Thanks,
-- 
HeteroDB, Inc / The PG-Strom Project
KaiGai Kohei <kaigai@heterodb.com>