Break Custom Buildsystem Plugin apart into 2 pieces.

[Sergey Kalinichev]

Hi,

While working on https://bugs.kde.org/show_bug.cgi?id=329788 bug, I came 
across the Custom Buildsystem Plugin that already implements this feature 
(define macros manually). After further investigation I've come to conclusion 
that reusing plugin's code could also solve the 
https://bugs.kde.org/show_bug.cgi?id=254662 bug. 

So here the questions:
1. What is it plugin for? Why is it disabled by default? (I had to modify 
*.kde4 file to enable it)
2. Do you think it's a good idea to refactor that pugin into 2 parts one of 
which will become "Custom Defines and Includes" plugin, that could be used by 
all project managers (or directly by language plugins?) to retrieve custom 
includes/defines?
3. If it's, where to store includes/defines then? Currently we use 
.kdev_include_paths, but Custom Buildsystem uses *.kde4 file for that. So which 
one to choose?

--
Regards,
Sergey