Sync FSX with FSFS:
Record-only merge r1603485 from libsvn_fs_fs and adapt it to FSX.

While the original change is not relevant to FSX, merging this
keeps the hotcopy.c code structure closer to FSFS.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1634962 13f79535-47bb-0310-9956-ffa450edef68