Prefer versioned Lua interpreter if it exists.
Prefer versioned Lua interpreter if it exists.

This avoids in practice a problem that occurs in this scenario:

1. user installs Lua 5.1, gets lua and lua5.1 binaries
2. user installs LuaRocks, it detects and uses lua
3. user installs Lua 5.2, gets lua and lua5.2 binaries (lua is replaced)
4. user installs LuaRocks with --lua-version=5.2, it detects and uses lua
5. luarocks-5.1 now uses lua, which is Lua 5.2, rockspecs get passed the wrong value of $(LUA)

luarocks/luarocks,tarantool/luarocks,robooo/luarocks,robooo/luarocks,keplerproject/luarocks,xpol/luavm,xpol/luarocks,xpol/luarocks,robooo/luarocks,robooo/luarocks,keplerproject/luarocks,xpol/luavm,xpol/luainstaller,tarantool/luarocks,keplerproject/luarocks,xpol/luainstaller,xpol/luavm,luarocks/luarocks,xpol/luainstaller,xpol/luavm,tarantool/luarocks,xpol/luarocks,luarocks/luarocks,keplerproject/luarocks,xpol/luarocks,xpol/luainstaller,xpol/luavm