Fix failing Jenkins build.

I forgot to DROP TABLE (IF EXISTS).
Merge pull request #27 from agouge/fix-jenkins-build

[Quick fix] Fix failing Jenkins build
Add ST_XMax
Add ST_XMin, ST_YMin and ST_YMax
Add ST_ZMin and ST_ZMax
Merge pull request #28 from agouge/min-max-fns

Add ST_XYZMinMax