lua: push characters as unformatted 1-character strings

Since Lua 5.3 the "%c" format character in lua_pushfstring will produce
the string "<\XXX>" (XXX being a decimal code sequence) when
given unprintable characters.

Use lua_pushlstring instead to reproduce the old behavior.

Lib/lua/lua.swg

@@ -185,7 +185,7 @@ use %include <std_except.i> instead
 
 // char is changed to a string
 %typemap(throws) char
-%{lua_pushfstring(L,"%c",$1);SWIG_fail;%}
+%{lua_pushlstring(L,&$1,1);SWIG_fail;%}
 
 /*
 Throwing object is a serious problem:

Lib/lua/luarun.swg

@@ -1841,7 +1841,10 @@ SWIG_Lua_InstallConstants(lua_State *L, swig_lua_const_info constants[]) {
       break;
     case SWIG_LUA_CHAR:
       lua_pushstring(L,constants[i].name);
-      lua_pushfstring(L,"%c",(char)constants[i].lvalue);
+      {
+        char c = constants[i].lvalue;
+        lua_pushlstring(L,&c,1);
+      }
       lua_rawset(L,-3);
       break;
     case SWIG_LUA_STRING:

Lib/lua/luatypemaps.swg

@@ -122,14 +122,14 @@ SWIGINTERN int SWIG_lua_isnilstring(lua_State *L, int idx) {
 %{$1 = (lua_tostring(L, $input))[0];%}
 
 %typemap(out) char
-%{  lua_pushfstring(L,"%c",$1); SWIG_arg++;%}
+%{  lua_pushlstring(L, &$1, 1); SWIG_arg++;%}
 
 // by const ref
 %typemap(in,checkfn="SWIG_lua_isnilstring",fragment="SWIG_lua_isnilstring") const char& (char temp)
 %{temp = (lua_tostring(L, $input))[0]; $1=&temp;%}
 
 %typemap(out) const char&
-%{  lua_pushfstring(L,"%c",*$1); SWIG_arg++;%}
+%{  lua_pushlstring(L, $1, 1); SWIG_arg++;%}
 
 // pointers and references
 // under SWIG rules, it is ok, to have a pass in a lua nil,