i18n 6.x-1.6

Fixed multiple issues:
- Fixed: issues with i18nvariables, do not check anymore i18n_variables on initialization, by Jose, #850708
- Fixed: Menu item's language is lost after node update, by neochief, #514630
- Fixed: PHP notices, by eMPee584, #769318
- Delete description on menu item delete, #844208 by plach
- Fixed: Node type help not translated, by NaX, #685788
- Some improvements to i18nmenu API, by plach, #386372
- Renamed theme_taxonomy_term_page() to theme_i18ntaxonomy_term_page() to avoid namespace conflicts
- Added some taxonomy API functions: i18ntaxonomy_translate_term_name()....
- Fixed: Access denied to database query (LOCK TABLES) on i18n_variable_set(), #769260
- Reworked variable initialization to fix multiple issues (front page, etc), #826774
- Some changes to variables API, added new function: i18n_variable_get()
- Fixed: Node type help not translated, by NaX, #685788
Preparing for D7 branch