Disallow indexing of your site on non-production environments

Disallow indexing of your site on non-production environments
fixed issue #70 - updated wordpress to 3.9.1
Merge pull request #71 from Jan1337z/master

Update WordPress to 3.9.1
Merge pull request #59 from roots/disallow-indexing

Disallow indexing when environment isn't production
Add optional DB_PREFIX configuration option
Merge pull request #78 from iloveitaly/db-prefix

Add optional DB_PREFIX configuration option