Undoubtably this may cause problems later if unchecked.
```
2016-03-22 21:57:52: WARNING[Server]: Assignment to undeclared global "options" inside a function at .../sofar/git/minetest/bin/../builtin/game/chatcommands.lua:862.
```
I've written several experimental bits of code that revolve around the
need for a consistent calendar, but implementing one is extremely hard
in mods due to time changes and mods overriding core.get_timeofday(),
which will conflict.
The second part of the problem is that doing this from a mod requires
constant maintenance of a settings file.
An implementation in core is trivial, however, and solves all of
these problems at virtually no cost: No extra branches in server
steps, and a single branch when minetest.set_time_of_day(), which is
entirely reasonable.
We store the day_count value in env_meta.txt.
The use case is obvious: This change allows mods to create an actual
virtual calendar, or properly account for seasonal changes, etc..
We add a "/days" chatcommand that displays the current day count. No
permissions are needed. It can only retrieve the day count, not
modify it.
Config settings:
profiling = true/false (gather statistics)
detailed_profiling = true/false (break mod times to callbacks)
Chat commands:
save_mod_profile saves current statistics in debug.txt and shows on console (on default loglevel)
