In conjunction with the issue #8108 on checking the loaded extensions, this pull request changes the check functions (ie in_array and get_extensions_loaded) by extension_loaded which is case insensitive.
This occurred in the systemCheck action for files PhpExtensionsCheck.php and DbAdapterCheck.php and in the databaseSetup action for files Mssql.php, Pgsql.php and Mysql.php.
This request also fixes a verification problem of the directive "always_populate_raw_post_data" which is considered as a boolean by HHVM (see http://docs.hhvm.com/manual/en/ini.core.php#ini.always-populate-raw-post-data).
Below are two screenshots showing the result before and after. You may also notice that the verification of the Reflection extension is present again (They are in french but the name of the extensions doesn't change).
Thanks @Loscillo for the pull request and improving HHVM support in Piwik #4415