Removed dropTStable() from the API. It is now handled by 
   removeTSdbTables() in package TSsql.
Some additional namespace cleanup in tests files.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/tsdbi@512 edb9625f-4e0d-4859-8d74-9fd3b1da38cb