Add a svn_repos_authz_parse() function which parses an authz config from a stream.
This also switches most testing of the authz code to using streams, which should result in a tiny bit faster testing since we're not needing to do disk I/O.
* subversion/libsvn_repos/authz.c (svn_repos__authz_read): Factor out walking the config for authz errors into ... (authz_validate): New function. (svn_repos_authz_parse): New function.
* subversion/include/svn_repos.h (svn_repos_authz_parse): New function.
* subversion/tests/libsvn_repos/repos-test.c (authz_get_handle): Adjust to allow authz conf to be optionally written to a in memory stream rather than always going to a temp file. (authz): Change most of the tests to use in memory streams and duplicate one test so that the code that is unique to the file path is excercised. (commit_editor_authz,issue_4060): Use in memory streams.