configure: Fix gnulib/crypto/md4 dependency

Gnulib project needs Autoconf to be able to import their modules with gnulib-tool
http://www.gnu.org/software/gnulib/manual/html_node/Initial-import.html#Initial-import

We only need md4.c file so this is a workaround to compile it without using
gnulib-tool --import

SoObjects/SOGo/.gitignore

@@ -0,0 +1,2 @@
+config.h
+md4.c

SoObjects/SOGo/GNUmakefile.preamble

@@ -30,6 +30,8 @@ SOGo_LIBRARIES_DEPEND_UPON += \
 ifeq ($(HAS_LIBRARY_gnutls),yes)
 ADDITIONAL_CPPFLAGS += -DHAVE_GNUTLS=1
 SOGo_LIBRARIES_DEPEND_UPON += -lgnutls
+ADDITIONAL_INCLUDE_DIRS += -I$(GNULIB_INCLUDE)
+SOGo_C_FILES += $(GNULIB_FILES)
 else
 ifeq ($(HAS_LIBRARY_ssl),yes)
 ADDITIONAL_CPPFLAGS += -DHAVE_OPENSSL=1