Add server side ncurses terminal

This adds a chat console the server owner can use for administration
or to talk with players.
It runs in its own thread, which makes the user interface immune to
the server's lag, behaving just like a client, except timeout.
As it uses the same console code as the f10 console, things like nick
completion or a scroll buffer basically come for free.
The terminal itself is written in a general way so that adding a
client version later on is just about implementing an interface.

Fatal errors are printed after the console exists and the ncurses
terminal buffer gets cleaned up with endwin(), so that the error still
remains visible.

The server owner can chose their username their entered text will
have in chat and where players can send PMs to.
Once the username is secured with a password to prevent anybody to
take over the server, the owner can execute admin tasks over the
console.

This change includes a contribution by @kahrl who has improved ncurses
library detection.

src/script/lua_api/l_server.cpp

@@ -45,6 +45,16 @@ int ModApiServer::l_get_server_status(lua_State *L)
 	return 1;
 }
 
+// print(text)
+int ModApiServer::l_print(lua_State *L)
+{
+	NO_MAP_LOCK_REQUIRED;
+	std::string text;
+	text = luaL_checkstring(L, 1);
+	getServer(L)->printToConsoleOnly(text);
+	return 0;
+}
+
 // chat_send_all(text)
 int ModApiServer::l_chat_send_all(lua_State *L)
 {
@@ -505,6 +515,8 @@ void ModApiServer::Initialize(lua_State *L, int top)
 	API_FCT(get_modpath);
 	API_FCT(get_modnames);
 
+	API_FCT(print);
+
 	API_FCT(chat_send_all);
 	API_FCT(chat_send_player);
 	API_FCT(show_formspec);

src/script/lua_api/l_server.h

@@ -46,6 +46,9 @@ private:
 	// the returned list is sorted alphabetically for you
 	static int l_get_modnames(lua_State *L);
 
+	// print(text)
+	static int l_print(lua_State *L);
+
 	// chat_send_all(text)
 	static int l_chat_send_all(lua_State *L);
 

src/script/lua_api/l_util.h

@@ -38,7 +38,7 @@ private:
 	// log([level,] text)
 	// Writes a line to the logger.
 	// The one-argument version logs to infostream.
-	// The two-argument version accept a log level: error, action, info, or verbose.
+	// The two-argument version accepts a log level.
 	static int l_log(lua_State *L);
 
 	// get us precision time