vocabs.parser: The manifest is now a definition observer, and updates itself when...

vocabs.parser: The manifest is now a definition observer, and updates itself when compilation units complete. This helps keep listener's search path up to date if vocabularies and words are renamed, defined, and undefined
- This makes forget-vocab more reliable in the listener
- It also fixes the problem of listener sessions where QUALIFIED: was used referring to outdated words if the vocabulary in question was reloaded