Merge the r1507382 group from trunk:

 * r1507382, r1509186, r1509196
   Allow passing NULL for the config dir to svn_config_walk_auth_data to use
   the default config dir path, like other functions handle this.
   Justification: all other APIs that take a config dir param allow NULL as
     meaning the default config path. Clients should not try to figure out
     that path themselves.
   Notes:
      r1509186 and r1509196 update the docstring accordingly.
   Votes:
     +1: steveking, philip, ivan, rhuijben


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.8.x@1513334 13f79535-47bb-0310-9956-ffa450edef68
Merge the r1513119 group from trunk:

 * r1513119, r1513122
   Correctly error out for large files in svn_diff_file_output_merge2() on
   32-bit platforms.
   Justification:
     Silently converting file size to apr_size_t is definitely wrong. Got
     related crashes in TortoiseSVN code.
   Votes:
     +1: ivan, philip, rhuijben


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.8.x@1513335 13f79535-47bb-0310-9956-ffa450edef68