Sync'ing FSX with FSFS:
Merge r1513874,1513880,1515329,1515331,1515516,1515534,1516429 from
/subversion/libsvn_fs_fs into subversion/libsvn_fs_x.  Conflicts were
related to FSFS refactoring.

This ports the revprop packing fixes.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1595106 13f79535-47bb-0310-9956-ffa450edef68