DB init script: re-add PLpgSQL language init and marker
DB init script: re-add PLpgSQL language init and marker

Both, the language initialization and the end marker, has been removed
in b1d77aa3, supposedly by accident. This commit re-adds it again.

htem/CATMAID,fzadow/CATMAID,fzadow/CATMAID,htem/CATMAID,fzadow/CATMAID,htem/CATMAID,fzadow/CATMAID,htem/CATMAID