Sync FSX with FSFS:
Merge revisions r1606142, r1606144 and r1606551 from libsvn_fs_fs and
resolve a minor text conflict.

This ports an index data initialization fix to FSX.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1635500 13f79535-47bb-0310-9956-ffa450edef68