Bump cache version due to other changes

This is not really needed. Cache corruption would be detected anyway.
But better safe than sorry.

src/modules/cache.c

@@ -59,7 +59,7 @@ static int    CacheLoadConfig  ( module_t *, FILE * );
 
 /* Sub-version number
  * (only used to avoid breakage in dev version when cache structure changes) */
-#define CACHE_SUBVERSION_NUM 15
+#define CACHE_SUBVERSION_NUM 16
 
 /* Cache filename */
 #define CACHE_NAME "plugins.dat"