bake: Abort "render first" jobs if we start using other pages. This prevents the baker from having one worker stuck on a very long job, like rendering the index page of a blog with lots and lots of posts.

# humanstxt.org/
# The humans responsible & technology colophon

# AUTHORS

Ludovic Chabant -- @ludovicchabant

# TECHNOLOGY

PieCrust -- http://bolt80.com/piecrust

# THANKS