mandatory LUAJIT conditional

[Jan Palus]

Hi,

in 1eeb8c7 
(http://git.savannah.nongnu.org/cgit/autoconf-archive.git/commit/?id=1eeb8c70a6dc8df17825260a22f9d9ee7115735d)
LuaJIT support was added with following comment:

#   Optionally a LUAJIT option may be set ahead of time to look for and
#   validate a LuaJIT install instead of PUC Lua. Usage might look like:
#
#     AC_ARG_WITH(luajit, [AS_HELP_STRING([--with-luajit],
#         [Prefer LuaJIT over PUC Lua, even if the latter is newer.
#         Default: no])
#     ])
#     AM_CONDITIONAL([LUAJIT], [test "x$with_luajit" != 'xno'])

The part about it being optional is not true though as if it's not given
(like many users do now) following statement fails:

  AM_COND_IF([LUAJIT],
          [_ax_lua_interpreter_list='luajit luajit-2.1.0-beta3 luajit-2.0.5 
luajit-2.0.4 luajit-2.0.3'],
          [_ax_lua_interpreter_list='lua lua5.4 lua54 lua5.3 lua53 lua5.2 lua52 
lua5.1 lua51 lua5.0 lua50'])

configure.ac:225: error: AM_COND_IF: no such condition "LUAJIT"
/usr/share/aclocal-1.16/cond-if.m4:23: AM_COND_IF is expanded from...
/usr/share/aclocal/ax_lua.m4:199: AX_PROG_LUA is expanded from...