Fix issue 1708 (part 1 of 2): Allow exporting of single files from working copy paths.
Fix issue 1708 (part 1 of 2):
Allow exporting of single files from working copy paths.

* subversion/libsvn_client/export.c
  (copy_one_versioned_file): New function, abstracted out from...
  (copy_versioned_files): ...here. Rearrange to deal with single files.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@852760 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion