editor: implement file batons The concept of current.file is incorrect, svn_delta.h documents open file lifetime as: * 5. When the producer calls @c open_file or @c add_file, either: * * (a) The producer must follow with any changes to the file * (@c change_file_prop and/or @c apply_textdelta, as applicable), * followed by a @c close_file call, before issuing any other file * or directory calls, or * * (b) The producer must follow with a @c change_file_prop call if * it is applicable, before issuing any other file or directory * calls; later, after all directory batons including the root * have been closed, the producer must issue @c apply_textdelta * and @c close_file calls. So, an open file can be kept open until after the root directory is closed and have deltas applied afterwards. In the meantime, other files may have been opened and patched, overwriting the current.file variable. This patch fixes it by introducing file batons bound to file paths, and using them to deduce the correct target in apply_textdelta(). In theory, open files could be put in a staging area until they are closed and moved in the RevisionData. But the current code registers files copied during a directory copy as open files and these will not receive a close_file() event. This separation will be enforced later.