This test can safely be ignored for other kinds of strings, but history string
contains separator after the last NUL byte and string containing NUL byte inside
thus means that separator will be placed at one position, but seeked at
another.
What works:
1. ShaDa file dumping: header, registers, jump list, history, search patterns,
substitute strings, variables.
2. ShaDa file reading: registers, global marks, variables.
Most was not tested.
TODO:
1. Merging.
2. Reading history, local marks, jump and buffer lists.
3. Documentation update.
4. Converting some data from &encoding.
5. Safer variant of dumping viminfo (dump to temporary file then rename).
6. Removing old viminfo code (currently masked with `#if 0` in a ShaDa file for
reference).