run_existing_command.py loads resources incorrectly on Windows

[keraJLi]

In run_existing_command.py, paths to the resources are built by using os.path.join. However, this should be done by something like sublime_lib.ResourcePath, because sublime_api uses its own path format. Therefore, running SublimeREPL on windows causes (at least for me) resources not to be found, because / and \ are mixed in the resource name. The same issue occured here.

[Thom1729]

If ST2 support is needed, posixpath.join would also probably work.