Language packs: No WPLANG anymore.

* The WPLANG constant is no longer needed. Remove define('WPLANG', ''); from wp-config-sample.php. Populate WPLANG option based on the WPLANG constant. When get_option('WPLANG') is an empty string it will override WPLANG.
* Introduce translations_api() which is available to communicate with the translation API. Move translation install related functions to a new file.
* Replace mu_dropdown_languages() with wp_dropdown_languages(). wp_dropdown_languages() is now populated by the translation API.
* Remove wp_install_load_language() and allow load_default_textdomain() to switch a core translation.

fixes #13069, #15677, #19760, #28730, #29281. 

git-svn-id: https://develop.svn.wordpress.org/trunk@29630 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/version.php

@@ -11,7 +11,7 @@ $wp_version = '4.0-beta4-29589-src';
  *
  * @global int $wp_db_version
  */
-$wp_db_version = 29188;
+$wp_db_version = 29630;
 
 /**
  * Holds the TinyMCE version