Table name length (maximum identifier length)

Hi,
I want CREATE TABLES WHICH HAVE a name length more than 31.
I change NAMEDATALEN in src/include/postgres_ext.h from 32 to 100 and
recompile the source code. I init the database and create a test base but
the maximum identifier length is still  31.
Can someone explain me what I must do to change this.
Thanks.
Mourad.