Problem: When updating viminfo with file marks there is no time order.
Solution: Remember the time when a buffer was last used, store marks for
the most recently used buffers.
Problem: When writing viminfo merging current history with history in
viminfo may drop recent history entries.
Solution: Add new format for viminfo lines, use it for history entries. Use
a timestamp for ordering the entries. Add test_settime().
Add the viminfo version. Does not do merging on timestamp yet.
Problem: New lines in the viminfo file are dropped.
Solution: Copy lines starting with "|". Fix that when using :rviminfo in a
function global variables were restored as function-local
variables.
