wftk core: list method adaptor

Just as the adaptor mechanism is a poor man's ActiveX, the list adaptor is a poor man's Recordset (see ADO). I'm taking everything Microsoft does and doing it more simply. Eventually I'll put them right out of business.

These are the functions exposed by a list adaptor, with many more to come, I'm sure:

Function	Parameters	Purpose
0: init		Initialize adaptor instance
1: free		Clean up instance before shutting down
2: info		Return XML describing the adaptor
3: create	List definition	Create a list.
4: destroy	List definition	Destroy a list.
5: add	List definition Object	Add an object to a list.
6: update	List definition Object	Update an object.
7: delete	List definition Key	Delete an object. If no key given, deletes current object in list.
8: get	List definition Key	Retrieve an object. If no key given, retrieves the current object.
9: query	List definition	Fills out the list definition with abbreviated records.
10: first	List definition	Iterates through a list. Note that the list defn is used as a cursor. Don't use the original!
11: next	List definition	Iterates.
12: prev	List definition	Iterates.
13: last	List definition	Iterates.
14: keygen	List definition Object	Builds a key from the object definition.
15: attach_open	List definition Key Field name (optional) name of local file	Opens an attachment stream for writing. The adaptor takes care of everything once the stream is closed. The localdir adaptor can use the name of local file to determine a filename for storage of the attachment (this makes it easy to treat, say, an images directory as a list with attachments.) The function returns a handle which can be decorated with a MIME type in content-type.
16: attach_write	Buffer to read from size number Handle	Writes data to an open attachment handle (like fwrite())
17: attach_close	Handle	Does the actual attachment; until attach_close is called, no effect is visible on the object. Among other things, the adaptor takes care of version control at this point.
18: attach_cancel	Handle	Closes the attachment handle with no effect on the object and no embarrassment.
19: retrieve_open	List definition Key Field name	Opens an attachment (or any other field for that matter) for reading. The handle is XML and is decorated with attributes 'size' and 'content-type'.
20: retrieve_read	Buffer to write to size number Handle	Reads data from an open attachment retrieval handle (like fread()).
21: retrieve_close	Handle.	Finishes a retrieval action.

Implementations:

• LIST_localdir (stores list data in files in directory)
• (TODO) LIST_db (list interface for RDBMS systems; uses underlying TASKINDEX adaptor)
• (TODO) LIST_lines (stores records as lines in a file; useful for conversion to/from CSV, etc.)