Make distcheck works

.gitmodules

 [submodule "foreign/zipflow"]
-	path = foreign/zipflow
+	path = src/foreign/zipflow
 	url = https://github.com/madler/zipflow.git

src/Makefile.am

-AM_CFLAGS = $(VARNISHSRC_CFLAGS) $(ZLIB_CFLAGS) -I../foreign/zipflow
+AM_CFLAGS = $(VARNISHSRC_CFLAGS) $(ZLIB_CFLAGS) -I$(srcdir)/foreign/zipflow
 
 # Modules
 
@@ -7,11 +7,12 @@ vmod_LTLIBRARIES = \
 
 libvmod_zipflow_la_LDFLAGS = $(VMOD_LDFLAGS) $(ZLIB_LIBS)
 libvmod_zipflow_la_SOURCES = \
+	foreign/zipflow/zipflow.c \
+	foreign/zipflow/zipflow.h \
 	vmod_zipflow.c \
 	zfr_iter.c \
 	zfr_iter.h
 nodist_libvmod_zipflow_la_SOURCES = \
-	../foreign/zipflow/zipflow.c \
 	vcc_zipflow_if.c \
 	vcc_zipflow_if.h
 
@@ -22,6 +23,8 @@ zfr_iter_test_CFLAGS = $(AM_CFLAGS) -DTEST_DRIVER
 zfr_iter_test_LDFLAGS = $(VMOD_LDFLAGS) $(ZLIB_LIBS) \
 	$(VARNISHSRC)/lib/libvarnish/libvarnish.la
 
+EXTRA_DIST = foreign/zipflow/LICENSE
+
 @BUILD_VMOD_ZIPFLOW@
 
 # Test suite