Improve picture distribution for Issue johnmckerrell#14

Changing size of grouping rectangle, so exactly FIND_IN_AREA_LIMIT fits
on the screen.

Signed-off-by: Radek Dostal <rd@radekdostal.com>

app/models/photo.rb

@@ -140,8 +140,8 @@ def self.find_in_area(bbox)
       return
     end
     bits.map! { |b| b.to_f }
-    lat_step = (bits[1] - bits[3]) / 400
-    lon_step = (bits[0] - bits[2]) / 300
+    lat_step = (bits[1] - bits[3]) / Math.sqrt(FIND_IN_AREA_LIMIT)
+    lon_step = (bits[0] - bits[2]) / Math.sqrt(FIND_IN_AREA_LIMIT)
     Photo.find( :all,
       :conditions => [
         "lat IS NOT NULL AND lon IS NOT NULL AND lat >= ? AND lat <= ? AND lon >= ? AND lon <= ? AND status = 'available'",