Allow to configure gitlab socket just by path

@jacobvosmaer noted that from user perspective it is not very handy to
have URL-encoded paths for sockets, and this way it is also not
consistent with everything else in GitLab where we use just
unix://path/to/socket instead of unix://path%2Fto%2Fsocket .

Be friends to users and allow them to configure socket path just with paths
with secondary gitlab_socket option, handler for which just encodes the
path and adds http+unix:// prefix, so internal handling is always by URL.

To protect from inconsistent input, configuration handler checks that
only one of gitlab_url or gitlab_socket can be given at a time.

NOTE CGI::escape() is used instead of URL::escape() because the latter
does not escape '/' characters by default:

    http://stackoverflow.com/questions/14989581/ruby-1-9-3-add-unsafe-characters-to-uri-escape

config.yml.example

@@ -13,8 +13,18 @@ user: git
 # only listen on a Unix domain socket. For Unix domain sockets use
 # "http+unix://<urlquoted-path-to-socket>/", e.g.
 # "http+unix://%2Fpath%2Fto%2Fsocket/"
+#
+# see also: gitlab_socket
 gitlab_url: "http://localhost:8080/"
 
+# Path to unix socket for gitlab instance.
+# Can be used instead of http+unix://... if one is not comfortable with
+# URL-encoding socket path in gitlab_url. Only one of gitlab_url or
+# gitlab_socket can be non-empty. Default to ""
+#
+# see also: gitlab_url
+gitlab_socket: ""
+
 # See installation.md#using-https for additional HTTPS configuration details.
 http_settings:
 #  user: someone

lib/gitlab_config.rb

 require 'yaml'
+require 'cgi'
 
 class GitlabConfig
   attr_reader :config
@@ -24,7 +25,20 @@ class GitlabConfig
   end
 
   def gitlab_url
-    @config['gitlab_url'] ||= "http://localhost/"
+    gitlab_url = @config['gitlab_url']
+    gitlab_socket = @config['gitlab_socket']
+    if !gitlab_url.empty?  &&  !gitlab_socket.empty?
+      raise "Only one of gitlab_url or gitlab_socket can be non-empty"
+    end
+    url = gitlab_url
+    if !url
+      if !gitlab_socket.empty?
+        url = "http+unix://#{CGI::escape(gitlab_socket)}/"
+      else
+        url = "http://localhost/"
+      end
+    end
+    url
   end
 
   def http_settings