Don't reconfigure and remake vips if it has been configured.
Don't reconfigure and remake vips if it has been configured.

This should use travis's cache where possible, saving 4 minutes on the travis build time.

DigitalSlideArchive/large_image,DigitalSlideArchive/large_image,DigitalSlideArchive/large_image,girder/large_image,girder/large_image,girder/large_image