To have hg completion under bash just download raw file from here
http://www.selenic.com/hg/file/11efa41037e2/contrib/bash_completion
and source it to your .bash_profile
[[ -s "$HOME/.bash_completion_hg" ]] && source "$HOME/.bash_completion_hg"
sudo port install bash-completion
To use bash_completion, add the following lines at the end of your .bash_profile:
if [ -f /opt/local/etc/bash_completion ]; then
. /opt/local/etc/bash_completion
fi