After reading the following Verse of the Holy Qur'an,

Those who commit unlawful sexual intercourse of your women - bring against them four [witnesses] from among you. And if they testify, confine the guilty women to houses until death takes them or Allah ordains for them [another] way.Qur'an 4:15

and the following Ahadith,

1. Narrated Jabir: A man from the tribe of Bani Aslam came to the Prophet while he was in the mosque and said, "I have committed illegal sexual intercourse." The Prophet turned his face to the other side. The man turned towards the side towards which the Prophet had turned his face, and gave four witnesses against himself. On that the Prophet called him and said, "Are you insane?" (He added), "Are you married?" The man said, 'Yes." On that the Prophet ordered him to be stoned to the death in the Musalla (a praying place). When the stones hit him with their sharp edges and he fled, but he was caught at Al-Harra and then killed. Al-Bukhari Volume 7: Book 63: Hadith 195.

2. 'Abdullah b. Buraida reported on the authority of his father that Ma'iz b. Malik al-Aslami came to Allah's Messenger (may peace be upon him) and said: Allah's Messenger, I have wronged myself ; I have committed adultery and I earnestly desire that you should purify me. He turned him away. On the following day, he (Ma'iz) again came to him and said: Allah's Messenger, I have committed adultery. Allah's Messenger (may peace be upon him) turned him away for the second time, and sent him to his people saying: Do you know if there is anything wrong with his mind. They denied of any such thing in him and said: We do not know him but as a wise good man among us, so far as we can judge. He (Ma'iz) came for the third time, and he (the Holy Prophet) sent him as he had done before. He asked about him and they informed him that there was nothing wrong with him or with his mind. When it was the fourth time, a ditch was dug for him and he (the Holy Prophet) pronounced judgment about him. He (the narrator) said: There came to him (the Holy Prophet) a woman from Ghamid and said: Allah's Messenger, I have committed adultery, so purify me. He (the Holy Prophet) turned her away. On the following day she said: Allah's Messenger, Why do you turn me away? Perhaps, you turn me away as you turned away Ma'iz. By Allah, I have become pregnant. He said: Well, if you insist upon it, then go away until you give birth to (the child). When she was delivered she came with the child (wrapped) in a rag and said: Here is the child whom I have given birth to. He said: Go away and suckle him until you wean him. When she had weaned him, she came to him (the Holy Prophet) with the child who was holding a piece of bread in his hand. She said: Allah's Apostle, here is he as I have weaned him and he eats food. He (the Holy Prophet) entrusted the child to one of the Muslims and then pronounced punishment. And she was put in a ditch up to her chest and he commanded people and they stoned her. Khalid b Walid came forward with a stone which he flung at her head and there spurted blood on the face of Khalid and so he abused her. Allah's Apostle (may peace be upon him) heard his (Khalid's) curse that he had hurried upon her. Thereupon he (the Holy Prophet) said: Khalid, be gentle. By Him in Whose Hand is my life, she has made such a repentance that even if a wrongful tax-collector were to repent, he would have been forgiven. Then giving command regarding her, he prayed over her and she was buried.
   Sahih Muslim: Book 17: Hadith 4206.

I am still confused whether Islam supports Honour killing. The woman in the second Hadith I mentioned above repented, but still she was stoned to death (not forgiven). On the other hand Allah says that Anyone who repents will be forgiven.

But whoever repents after his wrongdoing and reforms, indeed, Allah will turn to him in forgiveness. Indeed, Allah is Forgiving and Merciful. Qur'an 5:39

How am I to interpret this concept? Is this (the stories from the two Ahadith) not Honour Killing? Isn't it allowed in Islam?