Optimize table existence check

On large databases, running SHOW TABLES will return a large array.
Avoid grabbing and looping over that every time by checking the table
by name directly. See here for reference:

http://dev.mysql.com/doc/refman/5.5/en/information-schema-optimization.html
Merge pull request #323 from Symplicity/optimized_hasTable

Optimize table existence check