Specify DB encoding as utf8 rather than UTF-8

Specifying the charset as UTF-8 results in:
Unable to connect to MySQL database server! (Unable to connect to
database: SQLSTATE[HY000] [2019] Can't initialize character set UTF-8

Apparently the option was ignored before php 5.3.6 [1], but under current versions it causes the connection to fail. The mysql manual specifies 'utf8' as the name of the encoding, this appears to work fine.

[1] http://stackoverflow.com/questions/4361459/php-pdo-charset-set-names