More features for the IFDEF expert in GExperts

[dummzeuch 1387]

The IFDEF editor expert was added to GExperts in 2016 and improved again in the same year, to support symbols defined in include files.

Unfortunately sometimes an include file itself sometimes includes other files (e.g. jclNN.inc in the JEDI Code Library includes jedi.inc) which will usually add additional symbols which are then available for conditional compilation. But the IFDEF expert only listed symbols from the original include file.

This has irked me for a long time, ... (read on in the blog post)