Switch to VXL master branch.

Our VXL revision temporarily pointed to a fork of VXL while we were waiting for PRs to be accepted. They have now been accepted, so we can start tracking the main fork of the project.

@haocheng.liu Would you mind reviewing this merge request?

Do: test

This merge request has been queued for testing. Test results may be viewed on:

• CDash (master)
• Buildbot (master) (only visible from inside Kitware)

Branch-at-master: 79e0f1bf

+1

Do: merge

mentioned in commit e4c209e6

merged