Sync FSX with FSFS:  Merge revisions
r1603605, r1606840, r1622931, r1622937, r1622942, r1622959, r1622963,
r1622987, r1623373, r1623398, r1628392, r1628427, r1631196, r1631197,
r1631240, r1631548, r1631550 and r1633617 from libsvn_fs_fs and resolve
the usual text conflicts with FSX.

This ports the "parser hardening" patches to FSX.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1635870 13f79535-47bb-0310-9956-ffa450edef68