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: