r19585: Add support for some more standard IDL instructions:

r19585: Add support for some more standard IDL instructions:
 - `include' (replaces helper())
 - `import' (replaces depends())

Add support for parsing importlib() - importlib() is now ignored (with a
warning), but no longer causes syntax errors.

helper() and depends() are now marked deprecated and will cause warnings.
(This used to be commit 1ccab71cb8a9e3db9448b6679d01ad00e1c1e9a3)