1. Adding the write_zero diskops back to append micro-ops by default. However, these diskops are not omitted by the omit-one heuristic in standardized specifier, since omitting them doesn't have any effect. Other such things (for appends and truncates) are also not omitted.

2. For open(O_TRUNC | O_CREAT), not producing truncate micro-ops any more if the file does not previously exist.
Some around-the-corner trimming for the scratchpad_dir option.