Gemspec no longer depends on git.

The CI works by pulling down tarballs of Vagrant, and the gemspecs
depending on `git ls-files` were making it not work.

.gitignore

@@ -8,6 +8,7 @@ Vagrantfile
 .vagrant
 
 # Bundler/Rubygems
+*.gem
 .bundle
 pkg/*
 tags

vagrant.gemspec

@@ -27,12 +27,44 @@ Gem::Specification.new do |s|
   s.add_development_dependency "contest", ">= 0.1.2"
   s.add_development_dependency "minitest", "~> 2.5.1"
   s.add_development_dependency "mocha"
-  #s.add_development_dependency "sys-proctable", "~> 0.9.0"
+  # This has problems on Windows, we need to find a better way:
+  # s.add_development_dependency "sys-proctable", "~> 0.9.0"
   s.add_development_dependency "rspec-core", "~> 2.11.0"
   s.add_development_dependency "rspec-expectations", "~> 2.11.0"
   s.add_development_dependency "rspec-mocks", "~> 2.11.0"
 
-  s.files         = `git ls-files`.split("\n")
-  s.executables   = `git ls-files`.split("\n").map{|f| f[/^bin\/(.*)/, 1]}.compact
+  # The following block of code determines the files that should be included
+  # in the gem. It does this by reading all the files in the directory where
+  # this gemspec is, and parsing out the ignored files from the gitignore.
+  # Note that the entire gitignore(5) syntax is not supported, specifically
+  # the "!" syntax, but it should mostly work correctly.
+  root_path      = File.expand_path("../", __FILE__)
+  all_files      = Dir.chdir(root_path) { Dir.glob("**/{*,.*}") }
+  all_files.reject! { |file| [".", ".."].include?(File.basename(file)) }
+  gitignore_path = File.join(root_path, ".gitignore")
+  gitignore      = File.readlines(gitignore_path)
+  gitignore.map!    { |line| line.chomp.strip }
+  gitignore.reject! { |line| line.empty? || line =~ /^(#|!)/ }
+
+  unignored_files = all_files.reject do |file|
+    # Ignore any directories, the gemspec only cares about files
+    next true if File.directory?(file)
+
+    # Ignore any paths that match anything in the gitignore. We do
+    # two tests here:
+    #
+    #   - First, test to see if the entire path matches the gitignore.
+    #   - Second, match if the basename does, this makes it so that things
+    #     like '.DS_Store' will match sub-directories too (same behavior
+    #     as git).
+    #
+    gitignore.any? do |ignore|
+      File.fnmatch(ignore, file, File::FNM_PATHNAME) ||
+        File.fnmatch(ignore, File.basename(file), File::FNM_PATHNAME)
+    end
+  end
+
+  s.files         = unignored_files
+  s.executables   = unignored_files.map { |f| f[/^bin\/(.*)/, 1] }.compact
   s.require_path  = 'lib'
 end