* removed need to modify backend files. everything is controlled with

* removed need to modify backend files. everything is controlled with
config.php overrides.
* config.php file moved to config_default.php.
* site configuration can be stored in config/ or plugin's directories.
* added code that switches to change_password domain, if plugin is used in
1.4.x.
* merak curl test is moved to init function.
* use $cpw_ prefix for all configuration overrides in order to avoid using
generic names.

git-svn-id: https://svn.code.sf.net/p/squirrelmail/code/trunk/squirrelmail@9154 7612ce4b-ef26-0410-bec9-ea0150e637f0