fix 'make distcheck': add lookup.h to Makefile.am
diff --git a/sgsnemu/Makefile.am b/sgsnemu/Makefile.am
index 53de69e..f2f930d 100644
--- a/sgsnemu/Makefile.am
+++ b/sgsnemu/Makefile.am
@@ -8,4 +8,4 @@
 
 #sgsnemu_DEPENDENCIES = ../gtp/libgtp.la
 
-sgsnemu_SOURCES = sgsnemu.c tun.c tun.h cmdline.c cmdline.h ippool.h ippool.c syserr.h syserr.c lookup.c
+sgsnemu_SOURCES = sgsnemu.c tun.c tun.h cmdline.c cmdline.h ippool.h ippool.c syserr.h syserr.c lookup.c lookup.h