Don't allow changing of units of measurement in recipes when changing servings

[mavanmanen]

Currently when you change the servings for a recipe it will change the units for ingredients.
As an example: 960 ml of chicken stock for 8 servings becomes 4 4/5 dl for 4 servings instead of 480 ml.
Not only is the usage of fractions like 4/5 uncommon in the metric system and it should have translated to 4.8 dl, it is also much more preferable to keep using the original unit as put into the recipe.
Same should apply to other notations, 0.25 should not be changed to 1/4 and vice versa.