Add MySQLi Driver and use this as the default

MySQL driver in PHP5.5 is deprecated. This will be updated in Kohana 3.4

ping @eyedol hopefully you this should kill all deprecated errors :)
Fix PDO connections for unit tests

The unit test DB connection DSN reuses the kohana type, however mysqli
isn't a valid DB type, need to replace with mysql
Make import script use MySQLi too
Merge pull request #106 from ushahidi/mysqli

Add MySQLi Driver and use this as the default