Location of inc-folder should be defined only once

Would be nice to only change one variable if the inc-folder is placed somewhere else. That would also make the life of maintainers easier, that will have to place inc somewhere else - e.g. /usr/local/share/nopriv/inc.

Btw, you can take a look at my fpm makefile[1}.
With fpm[2] and the makefile from my bitbucket repo you can generate a packages for deb and rpm.

[1] https://bitbucket.org/brejoc/fpm-makefiles/src/tip/nopriv?at=default
[2]https://github.com/jordansissel/fpm/wiki