Upgraded to Nginx 1.6.1 & 1.7.4.
Updated index files with Nginx 1.6.1 and 1.7.4.  Removed 1.7.1.
Fixed bug handling version numbers with letters in them.
Added utility methods to load PHP versions and PHP extensions from the index files.
Modified tests to copy the index files.  These are now needed by the PHP extension.
Load PHP versions and PHP extensions into the context.
Added two methods, one to validate php version and one to validate php extensions.
Fixed formatting (flake8).
Added validation for PHP and extensions.
Added intl and opcache extensions (lucid only, for now).
Added opcache extension for PHP 5.5.
Updated list of supported extensions.
Updated indexes to have intl and opcache extensions for precise and trusty environments.