Merge all changes (r1072541 - r1078213) from the 
integrate-txdelta-caching branch.

These patches introduce caching of txdelta hunks
to reduce disk I/O in operations like dump / verify.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1078357 13f79535-47bb-0310-9956-ffa450edef68