Avoid unnecessary inter-processor interrupts by checking that writes are necessary

[zacikpa]

This PR adds a new option check_diff to the function commands.write_to_file. When set to True, the function checks whether the current value is equal to the one being written - if it is, the write is skipped.

The new option is disabled by default, but I enable it for plugin options where the write may cause an inter-processor interrupt even when the value does not change.