scanbd Code

- The meta backend would always look for the meta.so file in the directory it was compiled for
Added a callback to scanbd to retrieve the location where the backends are stored
- Reverted split of scanbuttond config dir and lib dir. Use lib dir only
- Major cleanup of Makefile.simple: added Makefile.conf that contains all configuration
This is included from all applicable Makefile.simple
- Rewrote install section of Makefile.simple. Adapted it to latest configuartion and
made it aware of whether scanbuttond is used and only install backends when applicable

This fix should solve the linking issues also on *BSD (tested on FreeBSD)

Fix linking issue for scanbuttond backends

- Do not try to load scanbuttond backend .so files from scanbuttond_backends_dir, use the fixed library path
- Corrected path where store backends

Moved expansion of the script variable to an absolute path in oder to avoid a memory leak

Removed superfluous assrt

Added initialization for variable

allways initialize all variables

Added secriptio of the include statement in scanbd.conf

Added support for include(file) in scanbd.conf