Allow the bold version to be detected by Fontconfig.

Fontconfig has code that skips PCF fonts with no encoded charset, which
happened to be the case for sqb.bdf. This prevented it from being detected
and used by any application that relies on Fontconfig.

Fix it by setting the CHARSET_ENCODING and CHARSET_REGISTRY properties just
like sq.bdf does.
Merge pull request #1 from rakuco/fontconfig-detection

Allow the bold version to be detected by Fontconfig.