Handle utf-8 properly

Fixes errors like:

  Caught exception in engine "Wide character in syswrite at /nix/store/498lwsrn5kkdh1q8kn3vcpd3457w6m7a-hydra-perl-deps/lib/perl5/site_perl/5.16.3/Starman/Server.pm line 547."

Note that these errors didn't happen if the database encoding was set
to SQL_ASCII (which was the case for hydra.nixos.org, explaining why
it didn't get these errors). However, now the encoding must be
UTF8. To change it, do:

  update pg_database set encoding = pg_char_to_encoding('UTF8') where datname = 'hydra';

src/lib/Hydra/View/TT.pm

@@ -6,6 +6,7 @@ use Hydra::Helper::Nix;
 
 __PACKAGE__->config(
     TEMPLATE_EXTENSION => '.tt',
+    ENCODING => 'utf-8',
     PRE_CHOMP => 1,
     POST_CHOMP => 1,
     expose_methods => [qw/buildLogExists buildStepLogExists jobExists/]);