Load extensions even when only using middleman-core. Also, use Bundler.require when available rather than scanning gems for extensions.

middleman-core/bin/middleman

@@ -46,6 +46,9 @@ rescue LoadError
   end
 end
 
+# Automatically discover extensions in RubyGems
+Middleman.load_extensions_in_path
+
 # Change directory to the root
 Dir.chdir(ENV["MM_ROOT"] || Dir.pwd) do
   

middleman-core/lib/middleman-core.rb

@@ -196,6 +196,9 @@ module Middleman
     #
     # @private
     def load_extensions_in_path
+      if defined?(Bundler)
+        Bundler.require
+      else
         extensions = rubygems_latest_specs.select do |spec|
           spec_has_file?(spec, EXTENSION_FILE)
         end
@@ -204,6 +207,7 @@ module Middleman
           require spec.name
         end
       end
+    end
 
     # Backwards compatible means of finding all the latest gemspecs
     # available on the system

middleman/lib/middleman.rb

@@ -3,6 +3,3 @@ require "middleman-more"
 
 # Make the VERSION string available
 require "middleman-core/version"
-
-# Automatically discover extensions in RubyGems
-Middleman.load_extensions_in_path