Enabled libknot to use log facilites for debugging.

Knot.files

src/Makefile.am

src/common/log.c

src/common/log.h

src/knot/common.h

src/knot/conf/cf-lex.l

src/knot/conf/conf.h

src/knot/conf/logconf.c

src/knot/other/debug.h

src/knot/server/dthreads.c

src/knot/server/zones.c

src/libknot/util/debug.h