Fix mixlib-archive on Windows, add Appveyor

Gemfile

@@ -28,3 +28,18 @@ instance_eval(ENV["GEMFILE_MOD"]) if ENV["GEMFILE_MOD"]
 # If you want to load debugging tools into the bundle exec sandbox,
 # add these additional dependencies into Gemfile.local
 eval_gemfile(__FILE__ + ".local") if File.exist?(__FILE__ + ".local")
+
+# These lines added for Windows (x64) development only.
+# For ffi-libarchive to function during development on Windows we need the
+# binaries in the RbConfig::CONFIG["bindir"]
+#
+# We copy (and overwrite) these files every time "bundle <exec|install>" is
+# executed, just in case they have changed.
+if RUBY_PLATFORM =~ /mswin|mingw|windows/
+  instance_eval do
+    ruby_exe_dir = RbConfig::CONFIG["bindir"]
+    assemblies = Dir.glob(File.expand_path("distro/ruby_bin_folder", Dir.pwd) + "/*.dll")
+    FileUtils.cp_r assemblies, ruby_exe_dir, verbose: false unless ENV["_BUNDLER_LIBARCHIVE_DLLS_COPIED"]
+    ENV["_BUNDLER_LIBARCHIVE_DLLS_COPIED"] = "1"
+  end
+end

appveyor.yml

@@ -0,0 +1,31 @@
+version: "master-{build}"
+
+os: Visual Studio 2017
+platform:
+  - x64
+
+environment:
+  matrix:
+    - ruby_version: "25-x64"
+
+clone_folder: c:\projects\mixlib-archive
+clone_depth: 1
+skip_tags: true
+branches:
+  only:
+    - master
+
+install:
+  - SET PATH=C:\Ruby%ruby_version%\bin;%PATH%
+  - echo %PATH%
+  - ruby --version
+  - gem --version
+  - gem update --system
+  - gem install bundler --quiet --no-ri --no-rdoc
+  - bundler --version
+
+build_script:
+  - bundle install
+
+test_script:
+  - bundle exec rake

lib/mixlib/archive.rb

@@ -49,14 +49,8 @@ def extract(destination, perms: true, ignore: [])
 
     private
 
-    BACKSLASH = '\\'.freeze
-
     def path_separator
-      if Gem.win_platform?
-        File::ALT_SEPARATOR || BACKSLASH
-      else
-        File::SEPARATOR
-      end
+      File::SEPARATOR
     end
 
     def create_and_empty(destination)