Add the conceal patch from Vince Negri.
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index c6d0b40..96a3a87 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -235,6 +235,7 @@
 #endif
 #ifndef FEAT_SYN_HL
 # define ex_syntax		ex_ni
+# define ex_ownsyntax		ex_ni
 #endif
 #ifndef FEAT_SPELL
 # define ex_spell		ex_ni