Disable gemdeps detection when building extensions

If an extension has an Gemfile or Isolate file RubyGems would try to
load this when building the extension.  This could cause failures if the
unsupported bundler API methods were used.

RubyGems now disables gemdeps file detection when building extensions.

Fixes #436

lib/rubygems/ext/builder.rb

@@ -44,7 +44,7 @@ def self.run(command, results, command_name = nil)
     verbose = Gem.configuration.really_verbose
 
     begin
-      #rubygems_gemdeps, ENV['RUBYGEMS_GEMDEPS'] = ENV['RUBYGEMS_GEMDEPS'], nil
+      rubygems_gemdeps, ENV['RUBYGEMS_GEMDEPS'] = ENV['RUBYGEMS_GEMDEPS'], nil
       if verbose
         puts(command)
         system(command)
@@ -53,7 +53,7 @@ def self.run(command, results, command_name = nil)
         results << `#{command} #{redirector}`
       end
     ensure
-      #ENV['RUBYGEMS_GEMDEPS'] = rubygems_gemdeps
+      ENV['RUBYGEMS_GEMDEPS'] = rubygems_gemdeps
     end
 
     unless $?.success? then