Core: limited levels of subdirectory hierarchy used for temp files. Similar to ngx_http_file_cache_set_slot(), the last component of file->name with a fixed length of 10 bytes, as generated in ngx_create_temp_path(), is used as a source for the names of intermediate subdirectories with each one taking its own part. Ensure that the sum of specified levels with slashes fits into the length (ticket #731).