This unifies the settings APIs.
This also unifies the sync and async registration APIs, since the async
registration API did not support adding non-functions to the API table.
* squashed: CSM: Implement register_globalstep
* Re-use fatal error mechanism from server to disconnect client on CSM error
* Little client functions cleanups
* squashed: CSM: add core.after function
* core.after is shared code between client & server
* ModApiUtil get_us_time feature enabled for client
The commit
8f9af57314f71aae1cc77e13f9996e13015d776d "Add core.get_dir_list" by @ShadowNinja
has removed the implementation of the l_get_dirlist function and all its usages
from the l_mainmenu.cpp file, but hasn't removed it from the header file.
The reason why this hasn't been detected earlier is that C++ has this interesting
feature to still make it possible to create instances of classes whose never used
private methods are declared but not defined.
Client now informs about incompatible servers from the list, this permits to prevent the protocol movements.
Server announces its supported protocol versions to master server
