drop the default max operations

the cache defaulted to 10,000 operations, fine for nip2, not fine for
batch-style applications

thanks Rafael

ChangeLog

@@ -13,6 +13,7 @@
 - removed embedded thumbnail reader from vipsthumbnail: embedded thumbnails
   are too unlike the main image
 - fix to vipsthumbnail --crop, thanks Alessandro 
+- reduce default cache size to 1,000 operations
 
 6/3/14 started 7.38.6
 - grey ramp minimum was wrong

libvips/iofuncs/cache.c

@@ -77,10 +77,12 @@ char *vips__cache_max_files = NULL;
 gboolean vips__cache_dump = FALSE;
 gboolean vips__cache_trace = FALSE;
 
-/* Max number of cached operations. We are likely to trim due to memuse or
- * file use before we hit this limit.
+/* Max number of cached operations. 
+ *
+ * It was 10,000, but this was too high for batch-style applications with
+ * little reuse. 
  */
-static int vips_cache_max = 10000;
+static int vips_cache_max = 1000;
 
 /* How many tracked open files we allow before we start dropping cache.
  */