Sync FSX with FSFS:
Merge r1601633, r1604720, r1604794, r1615356, r1628764 from libsvn_fs_fs
and resolve a few simple text conflicts caused by renamed functions.

These are various code simplifications as well as style and formatting
cleanups in tree.c.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1634956 13f79535-47bb-0310-9956-ffa450edef68