Fix the rebar wrapper on windows
Fix the rebar wrapper on windows

System.find_executable for rebar returns a rebar.cmd file, which should not
be wrapped by escript. We now have an extra check that verifies whether the
invoked file is indeed a cmd file.

kelvinst/elixir,elixir-lang/elixir,ggcampinho/elixir,gfvcastro/elixir,michalmuskala/elixir,antipax/elixir,kelvinst/elixir,lexmag/elixir,kimshrier/elixir,beedub/elixir,pedrosnk/elixir,pedrosnk/elixir,kimshrier/elixir,beedub/elixir,lexmag/elixir,gfvcastro/elixir,antipax/elixir,ggcampinho/elixir,joshprice/elixir