MAINTENANCE: Automated closing of pull requests.

This commit exists to close the following pull requests on Github:

Closes #1217 (requested by ankurdave, srowen)
Closes #4650 (requested by andrewor14)
Closes #5307 (requested by vanzin)
Closes #5664 (requested by andrewor14)
Closes #5713 (requested by marmbrus)
Closes #5722 (requested by andrewor14)
Closes #6685 (requested by srowen)
Closes #7074 (requested by srowen)
Closes #7119 (requested by andrewor14)
Closes #7997 (requested by jkbradley)
Closes #8292 (requested by srowen)
Closes #8975 (requested by andrewor14, vanzin)
Closes #8980 (requested by andrewor14, davies)