Support lua 5.3

[daurnimator]

Work with lua 5.3

Major new feature is integer support, this means the lua_int64 code can be dropped.

Currently these issues are present:

plluaspi.c: In function ‘luaP_cursorfetch’:
plluaspi.c:738:34: warning: implicit declaration of function ‘luaL_optlong’ [-Wimplicit-function-declaration]
   SPI_cursor_fetch(c->cursor, 1, luaL_optlong(L, 2, FETCH_ALL));
                                  ^
pllua_errors.c: In function ‘luaB_error’:
pllua_errors.c:16:17: warning: implicit declaration of function ‘luaL_optint’ [-Wimplicit-function-declaration]
     int level = luaL_optint(L, 2, 1);
                 ^

These should be easily solved by changing to luaL_optinteger

[mbalmer]

I changed these calls to luaL_optineger, PL/Lua should now work just fine on 5.3. The int64 stuff need inspection, though.