Fix server crashing on Lua errors

Previously, the server called FATAL_ERROR when a Lua error occured.
This caused a (mostly useless) core dump.
The server now simply throws an exception, which is caught and printed before
exiting with a non-zero return value.
This also fixes a number of instances where errors were logged multiple times.

src/mods.cpp

@@ -27,6 +27,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "settings.h"
 #include "strfnd.h"
 #include "convert_json.h"
+#include "exceptions.h"
 
 static bool parseDependsLine(std::istream &is,
 		std::string &dep, std::set<char> &symbols)