Typecast strings to integers for SQL against INTEGER columns

# Changes

* Typecasts `getParam` values for SQL `INT` columns with PHP `(int)`
* Maps PHP array values with `intval` when querying SQL `INT` columns
* Ensures optimal MySQL performance, as the query planner (seen in version 5.6.11) can perform full table scans when given string values for integer columns

# Tests

* Code review, please!
* No functionality or logical changes (`0` and `NULL` both evaluate false)