I'd like to be able to use a supplied build parameter in the SVN URL used to
checkout the code. Use case: I want to be able to trigger a build of a specific
revision through use of a build parameter b/c Google Code doesn't always send
its web hooks in the same order that the code is committed (i.e. you might
receive the web hook for r2 before the web hook for r1 and will end up building
r2 twice if just checking out trunk).