Initial groundwork to use phpdocumentor.

Initial groundwork to use phpdocumentor.
Added @package and @subpackage tags.
Some cases of define() for SM_PATH were tagged @ignore to reduce the number of phpdocumentor warnings - this may need to be done everywhere else, or removed where I've done it so far.  We'll see.

git-svn-id: https://svn.code.sf.net/p/squirrelmail/code/trunk/squirrelmail@6030 7612ce4b-ef26-0410-bec9-ea0150e637f0