Adds support to JSON parser in the nginx module

Building with --enable-standalone-module was failing due
the lack of the reference to the msc_json.c file inside the
standalone/Makefile.am. This patch also place the dependency
of the yajl to the nginx module config script.

nginx/modsecurity/config.in

@@ -7,7 +7,8 @@ CFLAGS="$CFLAGS \
     @LIBXML2_CFLAGS@ \
     @LUA_CFLAGS@ \
     @MODSEC_EXTRA_CFLAGS@ \
-    @PCRE_CFLAGS@"
+    @PCRE_CFLAGS@ \
+    @YAJL_CFLAGS@"
 
 
 CORE_LIBS="$CORE_LIBS \
@@ -18,7 +19,8 @@ CORE_LIBS="$CORE_LIBS \
     @LIBXML2_LDADD@ \
     @LUA_LDADD@ \
     @PCRE_LDADD@ \
-    @APXS_LIBS@"
+    @APXS_LIBS@ \
+    @YAJL_LIBS@"
 
 ngx_addon_name=ngx_http_modsecurity