thank you all for your help, i got solution, there was problem at server side, i was using openshift server for hosting, when i change ft_min_word_len file then in again next restart it will default changes value to 4.. i reported bug and got this reply
the "devenv" is a lightly built testing environment, a daily version.
also we have other testing environment like INT and STG, i guess you may test
on them even on PR environment.
INT -> is built from devenv;
STG -> is built from INT;
generally, the INT version is older than devenv, and the STG version is older than INT so if you test on INT and STG, we need to ensure the fixed is merged into them. as i know, the devenv may be merged to PR environment till January 2014.
if possible,you can have a try on devenv.