PATCH: Various issues.

First, thanks for the module - it's exactly what we needed for one of our sites. I installed it and got it working pretty easily, but in looking at the code I fixed the following issues:

• remove the use of globals and hook_init, the module should only execute code when needed and not pollute the global namespace.
• sanitize the type names when used in sql queries, to prevent SQL injection
• prevent linking to unpublished nodes
• use CCK API functions to get the synonyms table. This should be more robust that querying CCK tables directly, and it takes care of a bug I found. I had a synonyms field, with multiple values, only associated with one content type and this was causing a SQL error.