Allow zoom to actually show more data.

This allows the client to retrieve blocks at a greater distance
from the server, thus allowing for a real zoom.

src/util/numeric.h

@@ -232,6 +232,8 @@ u64 murmur_hash_64_ua(const void *key, int len, unsigned int seed);
 bool isBlockInSight(v3s16 blockpos_b, v3f camera_pos, v3f camera_dir,
 		f32 camera_fov, f32 range, f32 *distance_ptr=NULL);
 
+s16 adjustDist(s16 dist, float zoom_fov);
+
 /*
 	Returns nearest 32-bit integer for given floating point number.
 	<cmath> and <math.h> in VC++ don't provide round().