I suggest that you add a line to create the wikidb database to the top of buildusers.sql, like so:
CREATE DATABASE IF NOT EXISTS wikidb;
Just a convenience thing.
Also, could the INSTALL file explicitly say that buildusers.sql should be run as a mysql user who has the power to create databases and grant privileges, so typically you would run the script as the mysql (not necessarily the system user) "root"?
Also, please insert the following in INSTALL file:
mysql -p --user=root < buildusers.sql
Cheers!
Jonathan