In repos where dependencies are changing between branches, having the

checkout and patch steps run as part of the Travis CI script would

sometimes fail (for example, attempting to do builds of djblets on

release-1.0.x failed in install because it was trying to get

django-evolution 2.0, as required in the master branch).
Doing the checkout and patch in before_install makes a lot more sense,

because then we've got the full change in the working directory before

doing anything.

Ran a build of a change from djblets-1.0.x and saw that it got past the

initial install/setup steps, where before it didn't.