enable checkpoint only if VAGRANT_CHECKPOINT_ENABLE=1 is set

--- vagrant-1.7.1/lib/vagrant/environment.rb~	2015-02-01 20:31:59.000000000 +0200
+++ vagrant-1.7.1/lib/vagrant/environment.rb	2015-02-01 20:37:14.419051054 +0200
@@ -5,7 +5,6 @@
 require 'set'
 require 'thread'
 
-require "checkpoint"
 require 'log4r'
 
 require 'vagrant/util/file_mode'
@@ -134,12 +133,20 @@
       @checkpoint_thr = Thread.new do
         Thread.current[:result] = nil
 
+        # Must enable by env var
+        if ENV["VAGRANT_CHECKPOINT_ENABLE"].to_s != ""
+          @logger.info("checkpoint: not enabled from env var")
+          next
+        end
+
         # If we disabled checkpoint via env var, don't run this
         if ENV["VAGRANT_CHECKPOINT_DISABLE"].to_s != ""
           @logger.info("checkpoint: disabled from env var")
           next
         end
 
+		require "checkpoint"
+
         # If we disabled state and knowing what alerts we've seen, then
         # disable the signature file.
         signature_file = @data_dir.join("checkpoint_signature")
--- vagrant-1.7.3/vagrant.gemspec~	2015-08-19 15:49:31.000000000 +0300
+++ vagrant-1.7.3/vagrant.gemspec	2015-08-19 15:49:47.733344521 +0300
@@ -20,7 +20,6 @@
   s.add_dependency "erubis", "~> 2.7.0"
   s.add_dependency "i18n", ">= 0.6.0", "<= 0.8.0"
   s.add_dependency "listen", "~> 3.0.2"
-  s.add_dependency "hashicorp-checkpoint", "~> 0.1.1"
   s.add_dependency "log4r", "~> 1.1.9", "< 1.1.11"
   s.add_dependency "net-ssh", ">= 2.6.6", "< 2.10.0"
   s.add_dependency "net-sftp", "~> 2.1"