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
