Add X-ACE to build system

- Added --disable-xace to configure.ac and issue configure error if trying
   to build XC-Security without X-ACE
 - Added XACE #define to dix-config.h
 - Added X-ACE sources to Xext/Makefile.am

Xext/Makefile.am

@@ -65,6 +65,13 @@ if XINERAMA
 BUILTIN_SRCS += $(XINERAMA_SRCS)
 endif
 
+# X-ACE extension: provides hooks for building security policy extensions
+# like XC-Security, X-SELinux & XTSol
+XACE_SRCS = xace.c xace.h xacestr.h
+if XACE
+BUILTIN_SRCS += $(XACE_SRCS)
+endif
+
 # Security extension: multi-level security to protect clients from each other
 XCSECURITY_SRCS = security.c
 if XCSECURITY   
@@ -149,6 +156,7 @@ EXTRA_DIST = \
 	$(XV_SRCS) \
 	$(RES_SRCS) \
 	$(SCREENSAVER_SRCS) \
+	$(XACE_SRCS) \
 	$(XCSECURITY_SRCS) \
 	$(XINERAMA_SRCS) \
 	$(XEVIE_SRCS) \