* make zip_add return index of new file entry
* add functions to:
  . set compression method for new/changed entry
  . set last modification time for entry
  . read/set comment for file/archive
  . read/set EAs
  . parse/create some EAs?
  . read/set ASCII file flag
* document that zip_source_free must not be called after
  zip_{add,replace} was successful.
* do not compress if storing is smaller
------------------------------------------------ others
* regression tests (duplicate file names, unchange, .{200})
* zip_commit
* zip_replace_zip: allow rewinding
* API for (file and archive) comments
* API for extracting and setting extra fields
* zipcmp: add option for file content comparison
* support for zip64 (large file)

* append to files (for self-extracting files)
* add custom compression function support
* zip_replace_zip: remember compression method, recompress if different speced
* close even if error...
* update-zip (instead of close, reopen)
* support for old compression methods?????
------------------------------------------------ regression tests
* (add, replace)
	add to empty zip
	add to existing zip
	add w/ existing file name [E]
	replace ok
	replace w/ illegal index [E]
	replace w/ deleted name [E]
	unchange added/replaced file
* (close)
	copy zip file
	open copy
	rename, delete, replace, add w/ new name, add w/ deleted name
	close
	zipcmp copy expected
	remove copy
* (delete)
* (error_get)
* (error_get_sys_type)
* (error_to_str)
* (file_error_get)
* (file_strerror)
* (fopen_index)
	illegal index
* (get_name)
* (get_num_files)
* (rename)
* (replace)
* (source_buffer)
* (source_file)
* (source_filep)
* (source_free)
* (source_function)
* (source_zip)
* (stat)
* (stat_index)
* (strerror)
* (unchange)
* (unchange_all)