Switch all branches to use Dylan's piglit repo.

Piglit commits have a high impact on the test pool, because they
trigger test runs on all associated branches.  Mesa developers are
interested in flagging their own regressions, not the regressions that
occur in piglit.

Change mesa_10.2, mesa_10.3, and jekstrand branches to use a more
stable HEAD than origin/master.  Dylan plans to merge from origin
occasionally.