added missing header files for target dist

Makefile.in

@@ -24,7 +24,7 @@ SOURCES:= pdu.c net.c debug.c encode.c uri.c coap_list.c resource.c hashkey.c \
 OBJECTS:= $(patsubst %.c, %.o, $(SOURCES))
 HEADERS:=coap.h config.h debug.h pdu.h net.h encode.h uri.h coap_list.h mem.h \
 	str.h option.h bits.h uthash.h utlist.h resource.h hashkey.h async.h \
-	subscribe.h block.h
+	subscribe.h block.h address.h prng.h coap_time.h
 CFLAGS:=-Wall -Wextra -std=c99 -pedantic @CFLAGS@
 CPPFLAGS:=@CPPFLAGS@
 DISTDIR=$(top_builddir)/$(package)