Plugin changes for core TabCompletion updates.

Change-Id: Ibfe55b87e9bde40638f3b169153c653d59c6d6f0
Depends-On: I80df12d3494a651bc63117d26b1caf94771a51dd
Reviewed-on: http://gerrit.dmdirc.com/3863
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager