Did Abraham Serve His Guests Non-Kosher?

A question you might not have thought about, but plenty of other people have.

The question arises from this Genesis 18 (King James Bible version of verses 1-15 below):

1. And the LORD appeared unto him in the plains of Mamre: and he sat in the tent door in the heat of the day;
2. And he lift up his eyes and looked, and, lo, three men stood by him: and when he saw them, he ran to meet them from the tent door, and bowed himself toward the ground,
3. And said, My Lord, if now I have found favour in thy sight, pass not away, I pray thee, from thy servant:
4. Let a little water, I pray you, be fetched, and wash your feet, and rest yourselves under the tree:
5. And I will fetch a morsel of bread, and comfort ye your hearts; after that ye shall pass on: for therefore are ye come to your servant. And they said, So do, as thou hast said.
6. And Abraham hastened into the tent unto Sarah, and said, Make ready quickly three measures of fine meal, knead it, and make cakes upon the hearth.
7. And Abraham ran unto the herd, and fetcht a calf tender and good, and gave it unto a young man; and he hasted to dress it.
8. And he took butter, and milk, and the calf which he had dressed, and set it before them; and he stood by them under the tree, and they did eat.
9. And they said unto him, Where is Sarah thy wife? And he said, Behold, in the tent.
10. And he said, I will certainly return unto thee according to the time of life; and, lo, Sarah thy wife shall have a son. And Sarah heard it in the tent door, which was behind him.
11. Now Abraham and Sarah were old and well stricken in age; and it ceased to be with Sarah after the manner of women.
12. Therefore Sarah laughed within herself, saying, After I am waxed old shall I have pleasure, my lord being old also?
13. And the LORD said unto Abraham, Wherefore did Sarah laugh, saying, Shall I of a surety bear a child, which am old?
14. Is any thing too hard for the LORD? At the time appointed I will return unto thee, according to the time of life, and Sarah shall have a son.
15. Then Sarah denied, saying, I laughed not; for she was afraid. And he said, Nay; but thou didst laugh.

This is a confusing passage. Christians like to ask the question: how many people visited Abraham? But I don't think they have any particular interest in the meal. But notice that these visitors were served "butter, and milk, and the calf which he had dressed, ... and they did eat": doesn't sound too kosher, does it? Well, there are a variety of answers to be found at this link (originally found here). My favourite is the idea that the angels did indeed eat non-kosher food and Moses used that to catch them out many years later, when getting hold of the Torah. 

All of which goes to show what different things different people with different traditions find in the same text. You can also imagine how different the reactions would be if someone wrote that passage now: Borges and Pierre Menard  spring to mind.