Get rid of the ever increasing number of private apis in svn_sorts.h by adding a new private/svn_sorts_private.h file with the private parts and updating the needed #include-s. *AND* Improve error reporting during xml parsing in ra_serf a bit.
For 1.9 the number of private apis in this public header more than doubled, doubling the original filesize, while our policy is to never add private functions in public headers.
* build.conf (libsvn_subr): Add export.
* subversion/include/private/svn_sorts_private.h New file, copied from ../svn_sorts.h.
* subversion/include/svn_sorts.h Remove everything possible in our private namespace. Keeping some references.