Add .gitignore for hpc temp files
Call TestImports tests & use withConnection

TestImports was not being called and showed up as uncovered in
coverage reports.  I didn't mean it to be runnable originally, but
let's just run it to make it go away from the uncovered list.
Remove withConn from tests
Add tests for Null param conversion
Extend FromRow/ToRow instance testing to longer tuples
Fix types in error messages
Fix typos in test assert strings by removing them