Support Enterprise over HTTP via `protocol` config option

Example `~/.config/hub`:

  my.example.org:
  - user: myuser
    oauth_token: mytoken
    protocol: http

Currently there is no way to set `protocol` other than manually editing the
configuration file.

features/fork.feature

@@ -135,3 +135,18 @@ Scenario: Related fork already exists
     And "git.my.org" is a whitelisted Enterprise host
     When I successfully run `hub fork`
     Then the url for "mislav" should be "git@git.my.org:mislav/dotfiles.git"
+
+  Scenario: Enterprise fork using regular HTTP
+    Given the GitHub API server:
+      """
+      before {
+        halt 400 unless request.env['HTTP_X_ORIGINAL_SCHEME'] == 'http'
+        halt 401 unless request.env['HTTP_AUTHORIZATION'] == 'token FITOKEN'
+      }
+      post('/api/v3/repos/evilchelu/dotfiles/forks', :host_name => 'git.my.org') { '' }
+      """
+    And the "origin" remote has url "git@git.my.org:evilchelu/dotfiles.git"
+    And I am "mislav" on http://git.my.org with OAuth token "FITOKEN"
+    And "git.my.org" is a whitelisted Enterprise host
+    When I successfully run `hub fork`
+    Then the url for "mislav" should be "git@git.my.org:mislav/dotfiles.git"

features/steps.rb

@@ -25,10 +25,12 @@ Given(/^the "([^"]*)" remote has url "([^"]*)"$/) do |remote_name, url|
   end
 end
 
-Given(/^I am "([^"]*)" on ([\w.-]+)(?: with OAuth token "([^"]*)")?$/) do |name, host, token|
+Given(/^I am "([^"]*)" on ([\S]+)(?: with OAuth token "([^"]*)")?$/) do |name, host, token|
   edit_hub_config do |cfg|
     entry = {'user' => name}
     entry['oauth_token'] = token if token
+    host = host.sub(%r{^([\w-]+)://}, '')
+    entry['protocol'] = $1 if $1
     cfg[host.downcase] = [entry]
   end
 end

lib/hub/github_api.rb

@@ -246,6 +246,7 @@ module Hub
       end
 
       def configure_connection req, url
+        url.scheme = config.protocol(url.host)
         if ENV['HUB_TEST_HOST']
           req['Host'] = url.host
           req['X-Original-Scheme'] = url.scheme
@@ -473,6 +474,11 @@ module Hub
         end
       end
 
+      def protocol host
+        host = normalize_host host
+        @data.fetch_value(host, nil, :protocol) { 'https' }
+      end
+
       def value_to_persist(value = nil)
         @data.persist_next_change!
         value