Created an automated test for the /lib/bytes_by_prefix.c

Created a test for the bytes_by_prefix.c file in order to make sure that
everything works well and make it easy to test if some change breaks
something. The UNIT_TEST main method from lib/bytes_by_prefix.c has been
removed as it isn't needed anymore nor compiled by default. Necessary
changes in the makefiles have been done.

Signed-off-by: Marios Makris <marios.makris@gmail.com>
Acked-by: Cyril Hrubis <chrubis@suse.cz>
diff --git a/lib/Makefile b/lib/Makefile
index 661c0a1..453cf95 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -43,3 +43,4 @@
 	install -m $(INSTALL_MODE) "$(builddir)/$(@F)" "$@"
 
 include $(top_srcdir)/include/mk/lib.mk
+include $(top_srcdir)/include/mk/generic_trunk_target.mk