Sync FSX with FSFS:  Merge revisions
r1629854, r1629855, r1630067 and r1630070 from libsvn_fs_fs
and resolved the usual FSX conflicts.

This makes FSX consistently use centralized path constructors
and parser utilities.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1635963 13f79535-47bb-0310-9956-ffa450edef68