Add support for geometry field type in MySQL

Adds geometry to Database_MySQL::datatype()
Merge pull request #45 from rjmackay/3.3/develop

Add support for geometry field type in MySQL
Refs #4745
Ref #4668 and #4688: Added more info in docs on how to set the charset for PDO
Merge pull request #47 from rjd22/3.3/bugfix/more_info_on_docs_for_charset_pdo

3.3/bugfix/more info on docs for charset pdo
Add MySQLi Database driver (refs #3898)
Oops, fix transparent extension (refs #3898)