postgresql: explicitly initialize with utf8 encoding

If we d not explicitly specify utf8 as the encoding, the server will be initialized with ASCII encoding for the template1 database on Mountain Lion, which causes problems when trying to create new databases with UTF8 encoding.

Here is an example of what the ```rake db:create``` command in Rails results in without this change:

```
(in /home/fespinoza/Workspace/TLI)
PGError: ERROR:  new encoding (UTF8) is incompatible with the encoding of the template database (SQL_ASCII)
HINT:  Use the same encoding as in the template database, or use template0 as template.
: CREATE DATABASE "System_test" ENCODING = 'unicode'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.0.5/lib/active_record/connection_adapters/abstract_adapter.rb:207:in `rescue in log'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.0.5/lib/active_record/connection_adapters/abstract_adapter.rb:199:in `log'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.0.5/lib/active_record/connection_adapters/postgresql_adapter.rb:493:in `execute'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.0.5/lib/active_record/connection_adapters/postgresql_adapter.rb:572:in `create_database'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.0.5/lib/active_record/railties/databases.rake:92:in `rescue in create_database'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.0.5/lib/active_record/railties/databases.rake:39:in `create_database'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.0.5/lib/active_record/railties/databases.rake:33:in `block (2 levels) in <top (required)>'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:636:in `call'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:636:in `block in execute'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:631:in `each'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:631:in `execute'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:597:in `block in invoke_with_call_chain'
/home/fespinoza/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/monitor.rb:201:in `mon_synchronize'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:590:in `invoke_with_call_chain'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:583:in `invoke'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:2051:in `invoke_task'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:2029:in `block (2 levels) in top_level'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:2029:in `each'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:2029:in `block in top_level'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:2023:in `top_level'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:2001:in `block in run'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:1998:in `run'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/bin/rake:31:in `<top (required)>'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/bin/rake:19:in `load'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/bin/rake:19:in `<main>'
Couldn't create database for {"adapter"=>"postgresql", "encoding"=>"unicode", "database"=>"System_test", "pool"=>5, "username"=>"forellana", "password"=>nil}
PGError: ERROR:  new encoding (UTF8) is incompatible with the encoding of the template database (SQL_ASCII)
HINT:  Use the same encoding as in the template database, or use template0 as template.
: CREATE DATABASE "System_development" ENCODING = 'unicode'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.0.5/lib/active_record/connection_adapters/abstract_adapter.rb:207:in `rescue in log'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.0.5/lib/active_record/connection_adapters/abstract_adapter.rb:199:in `log'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.0.5/lib/active_record/connection_adapters/postgresql_adapter.rb:493:in `execute'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.0.5/lib/active_record/connection_adapters/postgresql_adapter.rb:572:in `create_database'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.0.5/lib/active_record/railties/databases.rake:92:in `rescue in create_database'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.0.5/lib/active_record/railties/databases.rake:39:in `create_database'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.0.5/lib/active_record/railties/databases.rake:35:in `block (2 levels) in <top (required)>'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:636:in `call'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:636:in `block in execute'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:631:in `each'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:631:in `execute'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:597:in `block in invoke_with_call_chain'
/home/fespinoza/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/monitor.rb:201:in `mon_synchronize'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:590:in `invoke_with_call_chain'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:583:in `invoke'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:2051:in `invoke_task'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:2029:in `block (2 levels) in top_level'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:2029:in `each'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:2029:in `block in top_level'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:2023:in `top_level'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:2001:in `block in run'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/lib/rake.rb:1998:in `run'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/gems/rake-0.8.7/bin/rake:31:in `<top (required)>'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/bin/rake:19:in `load'
/home/fespinoza/.rvm/gems/ruby-1.9.2-p180/bin/rake:19:in `<main>'
Couldn't create database for {"adapter"=>"postgresql", "encoding"=>"unicode", "database"=>"System_development", "pool"=>5, "username"=>"forellana", "password"=>nil}
```

More info:
http://stackoverflow.com/questions/5821238/rake-dbcreate-encoding-error-with-postgresql