GitHub now supports closing a pull request
Basically, you need to do the following steps:
- Visit the pull request page
- Click on the pull request
- Click the "close pull request" button
Example (button on the very bottom):
This way the pull request gets closed (and ignored), without merging it.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…