premium config/build fixes and cleanups

Set SHARE_DIR (cf #5639 3. bug)

Made freeradius checks conditional on the radius hook existence.

Find an usage or remove config.setup

Move m4_sinclude calls to top-level (it is an illusion to believe they can be conditional)

Cleanup Makefile.in

Investigate if distcheck with and without autoreconf works (aka Marcin's test). If not either fix and document as not working.