MAINTENANCE: Automated closing of pull requests.

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

Closes #3584 (close requested by 'pwendell')
Closes #2433 (close requested by 'pwendell')
Closes #1697 (close requested by 'pwendell')
Closes #4042 (close requested by 'pwendell')
Closes #3723 (close requested by 'pwendell')
Closes #1560 (close requested by 'pwendell')
Closes #3515 (close requested by 'pwendell')
Closes #1386 (close requested by 'pwendell')