Merge the remainder of the 10Gb branch into /trunk. This patch revs APIs and touches the UI. For a detailed description of each merged revision see the respective log entry.
* Implement zero-copy code path
r1388102: extend the FS vtable. Add a function that allows for processing file content in-situ. r1388195: Rev reporter API and attempt zero-copy reporting for files contents below a given threshold r1388202: Add --zero-copy-limit parameter to svnserve and pass it down to the reporter r1388205: update remaining callers to use svn_repos_begin_report3. r1388211: rename *_try_process_file_content *_try_process_file_contents. r1388362: Bugfix: try_process_file_contents code plus a handful of bugs masked by the first. r1388640: Bugfix: off-by-one in contents size.
* Implement delayed checking for client-side abortion
r1388375: Extend aready rev'ed APIs and add --error-check-internal option to svnserve.
* Tune ra_svn TX buffer handling
r1388643: tune ra_svn TX buffer usage by reducing the number of copy operations etc. r1388807: page-aligned I/O buffers.
* Finalize APIs and UI
r1390409: replace --zero-copy-limit and --error-check-internal with a single option (--client-speed) at UI level but keep internal APIs as they are r1390414: replace help string for the --client-speed parameter. r1390419: UI typo r1390955: Schedule API changes for 1.8 instead of 1.9.